Category Archives: CoCo

Tandy/Radio Shack TRS-80 Color Computer (CoCo)

Sub-Etha Software announces more 2018 Chicago CoCoFEST! plans


Sub-Etha Software announces more 2018 Chicago CoCoFEST! plans

Des Moines, Iowa – March 14, 2018 – Iowa-based Sub-Etha Software reveals more plans for the upcoming 2018 27th Annual “Last” Chicago CoCoFEST! to be held April 21 and 22, 2018 at the Heron Point Convention Center in Lombard, Illinois.

“The biggest news,” says Sub-Etha co-founder Allen Huffman, “is that we will have Jolt Cola to drink during the road trip to Lombard, and maybe enough extra to share during the event.”

Among the new offerings at this year’s event will be CoCoWiFi, an inexpensive internet modem device that allows connecting the CoCo up to a WiFi network for accessing remote internet sites using telnet and other protocols. Both fully assembled and do-it-yourself kits are expected to be available, with pricing to be announced at the show.

CoCoWiFi is pretty cool,” says Huffman. “It looks like an old-school Hayes Smartmodem and can be used on any model Color Computer with any terminal program. If the MC-10 has a terminal program, I bet it would work there too. The best part about it is if you don’t wanna buy it, you can spend about $10 and put one together yourself without any soldering. But we’ll be glad to sell you one for much more than that.”

Another new offering will be SirSound, the serial port multi-voice sound device. SirSound provides (1980s) arcade-quality background music and sound effects from BASIC. It uses built-in commands with no assembly language or special drivers needed.

“SirSound is one of the funnest things I have ever worked on this month,” adds Huffman. “You can play the Frogger theme song just by typing a PRINT command. I expect it could also play the Pac-Man theme, too, but we haven’t tested that, yet.”

SirSound is still under development, as well as SirSound S (6-voices in stereo), SirSound Plus (SirSound with the ability to play stereo digital files) and Sir Sound S Plus. There will also be an open-source SirSound Jr project made available. It will have the most of the same features as SirSound, but will be limited to just 1-voice tone music. Beep beep.

“We also will have a selection of new-old-stock Sub-Etha items in original packaging for those who like to collect useless 5 1/4: floppy disks with photocopied instructions stored in plastic baggies. Of course, master disk images of all this stuff has been uploaded to the Color Computer Archive and will be available for free, too.”

Be sure to drop by Sub-Etha Software’s table in the main exhibitor hall during the event.

About Sub-Etha Software

Sub-Etha Software was founded in Lufkin, Texas in 1990, as a partnership between Allen C. Huffman and Terry S. Todd. It made it’s first CoCoFest appearance at the First Annual Atlanta CoCoFest in 1990, and it’s first Chicago CoCoFest appearance at the First Annual “Last” Chicago CoCoFEST! in 1992. They may be contacted online at

About the Chicago CoCoFEST!

The 27th Annual “Last” Chicago CoCoFEST! is sponsored by the Glenside Color Computer Club of Illinois. They may be contacted online at

Allen Huffman
PO Box 7634,
Des Moines, Iowa
Ph: 515-999-0227


SirSound video demonstrations

One year ago, on March 9, 2017, Sub-Etha Software announced the Sir Sound CoCo Sound Card, today referred to as SirSound, without the space. Today we present to you the first public demonstration of the project.

SirSound demo 1- introduction

This 7-minute video walks through the basic concept of the device, and shows how easy it is to convert BASIC “PLAY” music to use the SirSound device.

SirSound demo 2 – polyphonic music

This 4-minute video shows how multi-voice music will be handled. It demonstrates 3-part harmony, and also a quick version of the Frogger arcade game theme music, all from BASIC.

More to come…

Proposing PreciousPak: The One Pak to Rule them All

“It is fun to reinvent the wheel. If it were not for folks doing this, we would never have built a better mouse trap…” – Some Dude

But when it comes to expansion cartridges (Paks) for the Tandy/Radio Shack TRS-80 Color Computer, what if we never had to reinvent the wheel again?

Programmable Hardware

These days, it is easy to make virtual hardware by the use of FPGAs and other such devices.  At a smaller level, there are already examples of expansion cartridges that have the ability to remap themselves into different I/O registers, all through software. This type of programmable hardware would be the basis of the PreciousPak.

PreciousPak artist’s rendering

Such hardware could, through software control, present itself at various I/O addresses within the CoCo’s memory map. This would allow it to appear at the same memory locations used by the RS-232 Pak, or the Orchestra-90 Pak, or anything else.

Then, the core hardware of the cartridge would be something like a programmable PIC chip or AVR (Arduino) processor, acting as an interface between the CoCo memory map and external hardware via SPI bus, I2C or TTL UART.

This is not intended to be a “one pak to do everything.” Think of it as the hardware equivalent of Jim Brain’s CoCoFLASH product. His smart flash Pak can be reprogrammed with various ROM Pak images, allowing it to act like any of those original ROM Paks. In the case of PreciousPak, it would require loading with custom firmware and adding the proper expansion hardware to it.

Here are some of the things PreciousPak could be easily made to do…

PreciousPak things.


The PreciousPak could have special firmware loaded on it’s processor to emulate the 6551 UART chip found in the the Deluxe RS-232 Program Pak. This code would fix the known bugs, and could implement an internal buffer allowing for better speeds without data loss. An inexpensive TTL-to-RS232 module would be plugged in to provide the standard RS-232 connector.


The PreciousPak could interface with a Digital-to-Analog converter, and map in to the Orchestra-90 I/O address, and become an Orchestra-90 Pak. For advanced use, the firmware might even be made to allow loading up an Orch-90 music file and have it play in the background while the CoCo does other things. (Orch-90+!)


Of course, the PreciousPak could interface with an SD card module or USB flash drive adapter and then have firmware to make it look like a Kenton or other SCS/IDE interface. This would allow it to leverage already-existing OS-9 drivers and builds of RGB-DOS. Depending on the capability of the core PreciousPak hardware, perhaps it could even be made to emulate the Western Digital 1773 floppy drive chipset and act like a true floppy drive, similar to how CoCoSDC currently works. (Though, I expect this would require much more capability than would be needed for most other devices, so why bother…)


Firmware could emulate the 6850 UART, used by various CoCo MIDI Interfaces. A simple TTL-to-MIDI adapter would be plugged in, giving MIDI ports. By making it look like a 6850 in the standard CoCo MIDI Pak address, it would instantly be compatible with all existing MIDI software.


Completely new sound hardware could be added, and the firmware could translate incoming commands as needed. Software written to use the Texas Instruments SN76489 chip (like in the GameMaster Cartridge by John Linville) could work on this sound pak, provided whatever native sound chip it used was similar, and the firmware translated the commands.

Perhaps firmware could exist to allow dynamically switching into different modes, to emulate the types of sound found in Roger Taylor’s CoCo on a Chip FPGA project, or Gary Becker’s CoCoFPGA project. Perhaps it could be made to provide some level of emulation of the Tandy Speech/Sound Pak.

Product or Service?

This common hardware design would allow more folks to come out with custom hardware. With dozens of types of expansion devices based on the same core board, manufacturing costs could be reduced. And, with many expansion add-ons being off-the-shelf parts (like adding .92 cent RS-232 adapter), the overall cost of many items would probably be a fraction of what a custom board would cost.

There are so many off-the-shelf devices available today that could be made into such a Pak… Real time clocks, camera modules, WiFi, etc.

And, for folks on a budget that might now want to buy multiple paks all set up for different devices, they could buy just the core board, and then several of the add-on interfaces. They’d have to swap out firmware and modules before they could use it, of course, but it would be possible.

I find it a very intriguing idea.

But, unless someone with the know-how steps forward to do it, it will remain just a proposal.

About the Name

I was calling it OnePak, but there is a company by that domain name.

How to load Zimodem firmware to an ESP8266 without Arduino IDE


  • 2018-02-25: Clarification on what ESP devices these instructions are currently limited to, per a comment from James J.
  • 2018-02-26: Added notes about versions for ESP-1, NodeMCU ESP8266-12E, and NodeMCU-32S modules.
  • 2018-02-27: Added link to Espressif tool for Windows that is supposed to do ESP32 modules (and also does ESP8266). If it works, I may update this just to use that one tool for both module types.
  • 2018-03-02: Removed second Windows option until I have confirmed how it works.

Updating ESP8266 / ESP32 Firmware

NOTE: These instructions are currently limited to devices like the NodeMCU ESP8266-12E and the NodeMCU-32S development kits:

An ESP8266 development board, available for under $9 from Amazon. (And much less from China!)

These devices have a built-in USB-to-Serial interface, so they can be plugged up to a Mac/PC over a USB cable for uploading firmware. However, the instructions probably will work with things like the ESP-1 module by using a USB programming device that interfaces it to USB.

ESP-1 module USB programming adapter.

Customized Zimodem firmware for all three of these platforms is now being created.

The excellent Zimodem firmware by Bo Zimmerman turns a low-cost ESP8266 module into a WiFi smart modem. One of the challenges users face is how to get this firmware installed on their module to begin with. I have been providing steps on how to install and configure the Arduino IDE so you can download the Zimodem source, build it, and load it.

But, if you aren’t a developer and don’t really want to go through that many hoops, you can take an existing firmware binary file and just load it directly.

Here are the steps as I know them, for Windows (with a nice GUI), or Mac OS X/Linux (command line).

Customized Zimodem Firmware images

I have a customized version of the Zimodem firmware on my server pre-built for the NodeMCU ESP8266-12E devkit, NodeMCU-32S devkit, and ESP-1 module. Download this firmware image here:

The versions will be named as follows:

  • zimodem.ino.generic-3.4.bin – for the ESP-1 module.
  • zimodem.ino.nodemcu-3.4.bin – for the NodeMCU ESP8266-12E development kit.
  • zimodem.ino.nodemcu-32s-3.4.bin – for the NodeMCU-32S development kit.

These names are the default names that the Arduino IDE creates, with the version number added.

Windows – ESP8266 NodeMCU Firmware Programmer

Download the NodeMCU flasher program. There is a 32-bit and 64-bit version:

NOTE: A different utility may be needed for ESP32. There is one that espressif (the ESP chip creator) provides that does both ESP8266 and ESP32. It is a .rar file, and when I downloaded it under Window 10, it ended up as a .man file (?). I had to rename that to .rar, and then find a RAR extractor (I used a free one from the Microsoft store). If you are using an ESP32, you may want to try this:


With your ESP8266 module plugged in (so it appears as a COM: port to Windows), open the NodeMCU flasher program and select that COM port:

On the Advanced tab, uncheck the default internal firmware (that is the option you would use to restore an ESP8266 module back to factory firmware), and browse to the new firmware in the second line. Checkbox that line, and set the start address to 0x0000.

ESP8266 Flasher for Windows – Config tab, for specifying the new firmware to load.

You might also go to the Advanced tab and increase the baud rate if you want the update to go faster. Once the binary file and COM port have been specified, return to the Operation tab and click Flash to begin the upload to the ESP8266.

ESP8266 Flasher for Windows – Operation tab, flashing in progress.

…and when complete…

ESP8266 Flasher for Windows – Operation tab, flashing complete.

You can now restart the ESP8266 module and it should be using the new firmware.

Windows – ESP8266/ESP32 Espressif Flash Download Tools V3.6.3

I have tested this tool on ESP8266, but not on ESP32 yet. I will update this section when I do. It requires more steps to install and setup, but may be what we have to use for ESP32. Running it offers four different parts it can flash:

Espressif Flash Download Tools V3.6.3 for ESP8266 and ESP32

I will update this tutorial when I have confirmed how to use this.

Mac and Linux – esptool

Install esptool (a Python script) and pySerial (a Python library for talking to the serial port):

easy_install esptool
easy_install pyserial

NOTE: I think I hadto run this as super user, “sudo easy_install esptool”.

Identify the serial port connected to the ESP module. This can be done from a shell (Linux) or the Terminal (Mac). On Mac, can look for devices that begin with “cu”:

alsmbpro:temp allenh$ ls /dev/cu*
/dev/cu.Bluetooth-Incoming-Port /dev/cu.HC-05A-DevB /dev/cu.SLAB_USBtoUART

If you do not know what to look for, you could do this command before plugging in the ESP8266, then again after you plug it in and see what appears. (On my system, I know I installed Silicon Labs drivers, so I recognized the “SLAB” name.)

On Linux, I think you need to do ls /dev/ttyS*. (I also saw an exemple using “setserial -g /dev/ttyS[0123]”).

Now that you know what serial port is connected to the ESP module,  run specifying that port, and the firmware image to use. On my system: -p /dev/cu.SLAB_USBtoUART --baud 460800 write_flash --flash_size=detect 0 zimodem.ino.nodemcu-3.4.bin

If it works, you should see something like this:

prompt$ -p /dev/cu.SLAB_USBtoUART --baud 460800 write_flash --flash_size=detect 0 zimodem.ino.nodemcu-3.4.bin v2.2.1
Detecting chip type... ESP8266
Chip is ESP8266EX
Uploading stub...
Running stub...
Stub running...
Changing baud rate to 460800
Configuring flash size...
Auto-detected Flash size: 4MB
Compressed 344528 bytes to 247587...
Wrote 344528 bytes (247587 compressed) at 0x00000000 in 5.8 seconds (effective 472.4 kbit/s)...
Hash of data verified.

Hard resetting...

You can now restart the ESP8266 module and it should be using the new firmware.

Over-the-Air Updates

Once you have this special build of the firmware, you will be able to do over-the-air updates. Make sure you configure your Zimodem for your WiFi network by going through the:


You can then use the command “AT&U” to see what the current version is. Bo is currently working on 3.4.

In stock Zimodem, firmware updates pull from Bo’s website for the two boards he support (the ESP-1, I think, and some flavor of ESP32). For my customized “CoCoWiFi” version, it will pull special builds from my website instead, and there are three different boards supported.

As I build new versions of this customized Zimodem firmware, I will place them on my server and you can type (from the Zimodem command mode):


That will get whatever version I have available. You should not need to do any more USB updates, unless something goes horribly wrong, or you want to go back to stock NodeMCU firmware.

Please let me know if this works for you.

CoCoWiFi and SirSound project updates

Things have been real busy lately at Sub-Etha Galactic Headquarters… Here are some updates:


The CoCoWiFi has been tested on the bitbanger serial port and things seem to work just fine.

On the RS-232 Pak, a modification was needed to make the pak actually receive data (forcing the carrier detect signal). This has been done by an easy soldering mod to the DB9 connector. The downside is that it does not provide true CD, and there is no support for hardware flow control or DTR to drop calls. For just a bit more, there are RS232-to-TTL adapters that provide hardware flow control, which might help for doing high speed transfers. However, the lack of carrier detect and DTR means they won’t work with a BBS like they should

Thanks to David Chesek, new RS232-to-TTL adapters were located that include all the signals. These would be the best choice for running with an RS-232 Pak. I have two different types of adapters, but have only done some initial testing. I was unsuccessful getting the first adapter to work. I plan to test the second version this week.

I hope to have a hardware announcement to make before the CoCoFEST!


I learned much while working on CoCoWiFi, so I returned to work on the previously “announced” SirSound project. I got everything wired up properly and was able to write a BASIC program to make it play tones. I also worked with John Strong and migrated the prototype over to an Arduino Nano (matching the original Arduino sound player board he sent me last year).

The next phases is to figure out the various modes that sound module will run in. I have proposed:

  1. Direct. This mode just passes bytes to the sound chip, the same way you might do with a POKE command if it was a memory-mapped chip. BASIC is very slow at ANDing and ORing bits to make the messages, which is how my test program works, but this could be heavily optimized. This mode is mostly here to allow someone to port over code that was written for one of the other platforms that use an on-board SN76489 sound chip, though some of the bit-blasting players would probably not work as well over slow serial.
  2. PLAY. This is the BASIC mode, that will simulate the PLAY command. You will be able to send a string of notes to SirSound and play them just as easy as in EXTENDED COLOR BASIC. There are a few things that have to be adapted, like support for the multiple channels of audio, and sub-strings. Last year, it was suggested to look at the MSX computer’s PLAY command for examples of how Microsoft did this very thing. I may follow that syntax. MSX also ads a PLAY() function that can tell is background audio is in progress, and we will be able to achieve the same results using the Printer Read/CD signal on the bitbanger port. I plan to also add some sequencing extensions so repeating music loops don’t have to be sent over and over again.
  3. Optimized. This mode would be for assembly programs, and would pack data into 8-bit values rather than longer ASCII strings.
  4. Interactive. I am planning on having a shell/command-line interface (CLI) available which could be accessed. It would be used for testing the device without needing to write a BASIC program.

More to come…


RS232 to TTL adapters with all signals, including DCD

I have been experimenting with hooking up low-cost ESP8266 WiFi modules to the Radio Shack Color Computer (or anything with an RS-232 port) using cheap RS232-to-TTL adapters. Most of these adapters only support 3-wire RS-232 (transmit, receive and ground). This is fine for most uses of the CoCo’s built-in Serial I/O port (bitbanger) since it is only a 4-pin DIN connector with TX, RX, GND and CD, and most things do not rely on carrier detect.

But, for the Deluxe RS-232 Program Pak, a hardware 6551 UART chip is used and that chip requires to see carrier detect before it will receive any data. A workaround is to simply tie some of the TTL converter pins together to make it always present DCD to the RS-232 Pak:

This works fine if you are just connecting to remote systems, but if you want to run a BBS, those often rely on carrier detect to know if a caller is online. If a caller disconnects without properly logging off, the system may sit there forever (worst case) or until some software timeout is reached and the system resets. During that time, it would be possible for the next person connecting to resume that session.

This was a real and common issue with BBSes back in the 1980s, for this very reason – lack of carrier detection.

Another issue is the lack of hardware flow control. There could be times when the ESP8266 could try to send data faster than the computer could process, and there is no way (other than XON/OFF, which can’t be used for binary transfers) to tell it to pause sending.

I have found RS232-to-TTL adapters that provided 5-wire signals (adding RTS and CTS), which is needed for this hardware flow control. Those are a bit more costly (I found one for $9 on Amazon), and still do not address the carrier detect issue.

Once again, David Chesek comes to the rescue. He located an adapter that supports all the RS-232 signals, including RI (ring indicator). It is available for $11.50 plus shipping from a company in Las Vegas called Pololu (and might even be manufactured there):

Pololu RS-232 to TTL adapter with all signals. (Photo taken from

I took a gamble (pun intended) and ordered a few. I will report back as soon as I receive them and have had a chance to try them out.

Meanwhile, knowing such a thing exists, I did more searching and found a similar one on e-Bay from a seller called MDFLY. They have them for $3.25 plus shipping, and are shipped from California:

eBay seller MDFLY RS-232 to TTL adapter with all signals. (Photo taken from their eBay listing.)

The board layouts are quite different, but the functionality should be similar. I will be comparing both of these (and noting shipping time) when I have them.

With either one of these boards, properly wired to additional pins on a full ESP8266 development module, it should be able to provide hardware flow control and carrier detect. (Sorry, the ESP-01 module only has two I/O pins, so we’d have to pick and choose what to support on that one — like DTR and DCD for BBS use, or CTS/RTS flow control.)

More to come…

CoCo RS-232 Pak to 3-wire (TX, RX and GND) RS-232 device.

The Radio Shack Deluxe RS-232 Operation Manual (Tandy).pdf for the Color Computer is based on a 6551 UART chip.  The Pak provided a DB-25 with the following signals:

  • 1 – Frame Ground (not used)
  • 2 – Transmit Data (TX)
  • 3 – Receive Data (RX)
  • 4 – Request to Send (RTS)
  • 5 – Clear to Send (CTS)
  • 6 – Data Set Ready (DSR)
  • 7 – Signal Ground (GND)
  • 8 – Carrier Detect (DCD)
  • 20 – Data Terminal Ready (DTR)

Built-in serial ports disappeared from modern computers a long time ago, but USB RS-232 adapters are available in case one is ever needed. For our 1980s Color Computer, RS-232 is one of the only available interfaces to the outside world.

The built-in 4-pin DIN connector (marked Serial I/O) is not a real serial port. Instead, it is just a set of pins that can be toggled on and off (to RS-232 voltage levels) through software. By writing software with the proper timing, this port can send out serial data. This technique is called “bit banging” and it was very common in systems of this era. (And, today, if you use an Arduino, the “SoftwareSerial” routines which turn any I/O pin into a serial port are doing the same thing.)

There are many modern things that use serial for communication, but they are doing so at chip-level voltages – called TTL level (transitor-transitor level). An example of this would be the I/O pins of a Raspberry Pi or Arduino. There are also a myriad of small devices that work over a TTL-level serial port, such as USB interfaces, WiFi modules, Bluetooth, and many more.

To interface one of these with an old computer with an RS-232 port, you can use an RS-232 to TTL adapter such as this one from Amazon:

RS232-to-TTL adapter.

Amazon Link

This device has a DB-9 RS-232 port on one side, and pins on the other that represent the common signals of Transmit (TX), Receive (RX), Ground (GND) and voltage. Voltage is usually 5v or 3.3v depending on the device and what it will connect to. (An Arduino UNO has 5v I/O pins. A Raspberry Pi and some other models of Arduino use 3.3v pins.) The adapter has to match. Some are smart, and adjust based on the voltage they are given. Thus, if you are hooking an RS-232 device to an Arduino, you would power this TTL adapter from a 5V pin of the Arduino, and it should operate at 5v. Some adapters claim to adjust, so if you hook them up to a 3.3v pin on an Raspberry Pi, they work at 3.3v. The RS-232 side should be the same (traditional RS-232 voltage levels) in either case.

I have recently been experimenting with devices such as the ESP8266, which is a tiny (and cheap!) module that provides WiFi for about $2, and interfaces with TTL level serial. Using the CoCo’s built-in Serial I/O (bitbanger port) and a cable, I was able to hook the CoCo to one of these RS-232 TTL adapters and then hook that to the ESP8266. It worked great, limited only by the baud rate of the bitbanger! (Most older CoCo 1/2 terminal programs could only go about 1200 baud. The CoCo 3 has at least one terminal program, Twilight Term, that can operate a 9600 through the bitbanger port.)

ESP8266 development board to RS232 converter.

Since the bitbanger port only has TX, RX, CD and GND (and CD is not really used unless software specifically uses it), hooking it up like this worked well. But, when trying to connect to the more robust RS-232 Pak (which can operate at speeds of up to 115200 baud), I ran into some problems.

The 6551 can transmit data just fine, but in order for it to receive, it expects to see a carrier detect signal (DCD). If you just hook up the RS-232 Pak cable to the TTL adapter, using only TX, RX, and GND, that signal will not be active and terminal programs will not read any of the incoming data. You can send, but not receive.

In order to make this work, you have to trick the RS-232 Pak into thinking there is a DCD signal. From exploring various mailing lists, Facebook groups, and web postings, I found several suggestions on how to do this. The overall method looked like this:

RS-232 port modification to make it operate without needing real DCD and other signals.

By tying certain lines together on the end that goes to the RS-232 Pak, the Pak will think there are signals present that really are not there. This makes it work, since it now thinks there is a carrier detect.

The above modification can be done on an RS-232 to TTL adapter with a soldering iron and a bit of wire. A small solder blob can be used to connect pins 7 (RTS) and 8 (RTS), then another blog can connect pins 1 (DCD) and 6 (DSR), then a jumper wire can be ran from that solder blob over to 4 (DTR).

Dave Chesek did a modification on is cable and it looked like this: (And apologizes to Dave if he isn’t proud of his soldering skills. They are much, much nicer than what I can do!)

David Chesek’s modification to the RS232-to-TTL adapter, connecting pins 7+8 (RTS+CTS) with solder, and pins 1+6+4 (DCD+DSR+DTR) with solder and a jumper wire.

Once that is done, you can use a DB25-to-DB9 cable (I ordered one from Amazon) and connect it to one of these RS232-to-TTL adapters (I ordered one from Amazon) using a gender changer (I ordered one from Amazon) or a serial cable that already had the proper ends on them. (The one I used was a Male to Female cable, so I needed the gender changer.)

This modification is enough to trick the RS-232 Pak into allowing receiving of data.

For those that don’t solder, you can also order some DB9-to-terminal block adapters like this:

DB9 adapters from Amazon.

Amazon Link

I picked up a pair for around $8 because I wanted to find out which of the various suggestions would actually work. Through process of elimination, I found that the DCD+DSR+DTR was needed, but RTS+CTS was not. (And, some RS-DOS terminal programs worked with just DCD+DTR, which was one of the suggestions I was given.)

I hooked up short jumper wires like this:

Minimal wiring required to get an RS-232 Pak to talk to a 3-wire RS-232 interface (TX, RX and GND).

For the CoCo’s RS-232 Pak, this works great for various RS-DOS programs I tested (Greg-E-Term, Ultimaterm) and OS-9/NitrOS-9 (Supercomm).

I had read that the RS-232 Pak won’t send without a certain signal being present, but from my experiments this week, this does not seem to be the case. Only the DCD situation must be taken care of.

With this information, you can now get an RS-232 Pak out to an RS232-to-TTL adapter and then hook up various devices. In the case of my ESP8266 experiments, I was powering the TTL adapter off the ESP8266 module. If I were trying to use something stand-alone, like an HC-05 bluetooth module, I would need an additional 5v or 3.3v power source to power the module and the adapter.

Let the games begin!


Help needed with 6551-based RS-232 Pak to 3-wire without DCD


  • 2018-02-05: Thanks to Dave Chesek, this issue has been solved. He took the wiring diagram below and modified his RS232-to-TTL adapter with a  bit of solder. He put a blob connecting pins 7 (RTS) and 8 (CTS), and then soldered together 1 (DCD) and 6 (DSR) then ran a jumper wire from those two over to 4 (DTR). It worked fine. My efforts to do this with jumper wires must not have been making good connection (perhaps one of my DB9 pin holes is not as deep – TX, RX and GND all worked fine with the jumper wires). I will do a bit more investigation to see what the minimum required. Thanks, Dave!
  • 2018-02-06: See the complete writeup.

The 6551 serial chip will not receive unless DCD is active. Modern adapters do not provide DCD. I am trying to find a way to do this so I can hook my WiFi device (which only has TX, RX and GND) to the RS-232 Pak.

I have been trying to jumper wires to fake the DCD signal but nothing has worked. I do not know if my Pak is defective, since I have nothing else to connect it to for testing,

Many sites suggest a wiring example like this:

Has anyone done this? Nothing modern has DCD so surely there is a simple solution figured out long ago.

WiFi CoCo for $15 (or for any retro computer with an RS-232 port)


  • 2018-02-04: Removed an apparently necessary step.
  • 2018-02-05: Added crude drawing showing how I wired things up.
  • 2018-02-25: Fixing board support URL to include “http”.

If you want to get your Tandy / Radio Shack Color Computer (CoCo) on the internet (or any other 80s computer with a serial port), here is a dirt cheap way you can do it.

Cheap WiFi: The Early Years

Just a few years ago, adding WiFi to an Arduino meant buying a $60 add-on. My solution at the time was to get a much cheaper Ethernet and then use a cheap TP-LINK WiFi router hooked to it. I later found a source for a $10 Ethernet shield that made the overall cost even lower.

In 2014, the internet lit up with the discovery of the ESP8266 – a complete “WiFi on a chip” solution for under $5! Initially, all documentation was in Chinese but folks managed to figure out how to use it and, as they say, the rest is history.

Today the ESP8266 family of products is used in all kinds of things. There are now internet-enabled light switches, and front-ends for 3-D printers, and many other devices that get online thanks to this low-cost solution.

And, this includes all these retro computing platforms!

Cheap WiFi: How To

If you want to experiment, you can order an ESP8266 development board from Amazon for $8.79. This contains the low-cost ESP8266 module and then runs out all the various connection to pins, and also has a USB-Serial adapter built in. This USB port allows you to plug it up to a Mac or PC and upload new firmware, or use the device directly through a serial connection.

Here is the module I purchased. You can find many variations, some costing more, and others costing less. I wanted one I could get direct from Amazon using 2-day Prime delivery, but if you don’t mind waiting, you can find a similar part shipped from China for about $4.

An ESP8266 development board, available for under $9 from Amazon. (And much less from China!)

Since my 1980s computers do not have a USB port, I needed a way to hook them up to the old-style RS232 serial port instead. For that, I bought a cheap RS232-to-TTL adapter. Here is the one I purchased for around $7, shipped from Amazon with 2-day Prime shipping. I see there are some for a few bucks less which might work just as well, and if you don’t mind waiting a few weeks to get something shipped from China, I have seen them for about .67 cents!

RS232-to-TTL adapter.

Now all I had to do was connect the two modules together using some jumper wires. I needed four wires to connect Voltage (mine needed 5v), Ground, Transmit and Receive. You can buy a bundle of these wires for just a few dollars.

Once connected, it looked like this:

ESP8266 development board to RS232 converter.

I can power the module using a standard micro USB cable and charger (just like you might already have for an Android phone or Raspberry Pi or some models of Arduinos).

After this, all I needed was a NULL Modem cable to connect that DB9 connector to the Serial I/O port of my Color Computer. In my case, I used a “Driverwire cable” which has a 4-pin DIN connector on one end and a DB9 on the other. I needed to use a NULL Modem adapter to get the signals talking.

ESP8266 ESP-12E devkit wired to DB9-to-TTL adapter and connected to a CoCo Drivewire (null modem) cable.

Cheap WiFi: ZIMODEM Software

The final step I needed to do was to install different firmware on the ESP8266. The firmware that comes on the module does allow you to type certain “AT” commands and connect to WiFi and remote systems, but I wanted something easier and more compatible. I found this ZIMODEM firmware:

This makes the ESP8266 look like an old-style Hayes Smartmodem. Instead of using commands to dial a phone number, the commands will “dial” a remote telnet BBS. i.e., instead of:

ATDT 515-555-1212

…you can dial a telnet connection:


There are new commands added to display all nearby WiFi base stations, and connect to them. There’s even a command to retrieve a file from a web server! You can find full documentation on the ZIMODEM website.

Any terminal program can be used to make these types of connections. You can also configure it to receive incoming connections, and when someone telnets to your IP address, you will see a “RING” (just like the smartmodems did) and can have the system answer. Yep, it would be very easy to put an old-school BBS on the internet with this!

I was able to use this to connect an old Radio Shack CoCo to a remote BBS using the Greg-E-Term terminal program over the bitbanger port at 1200 baud (oooh, speedy).

Building and Installing ZIMODEM

I got these steps from the Amazon page for the ESP8266 part I purchased. I have edited them with additional notes and links.

Instruction & Steps of How to use:

  1. Download the latest version of the Arduino IDE. Today, there are versions of the IDE that run in a web browser (I have not tried these), as well as ones available for Mac, Windows and Linux. I used one for Windows 10, downloaded from the Microsoft Store.
  2. Install the IDE. (Well, duh…)
  3. Configure the Arduino IDE with support for the ESP8266:
    1. Go to File->Preferences and copy the URL below to get the ESP board manager extensions:
    2.  Go to Tools > Board > Board Manager> Type “esp8266” and download the Community esp8266 and install.
    3. Set up your chip as:
      • Tools -> Board -> NodeMCU 1.0 (ESP-12E Module)
      • Tools -> Flash Size -> 4M (3M SPIFFS)
      • Tools -> CPU Frequency -> 80 Mhz
      • Tools -> Upload Speed -> 921600
      • Tools–>Port–> (whatever it is)
  4. Download and run the ESP8266 flasher program from Github:Win 32-bit:
  5. To test that things are working, in Arduino IDE, look for the old fashioned Blink program (File->Examples->ESP8266->Blink). Load, compile and upload. If it worked, the module will have a blinking LED, indicating it is now running software you build using the Arduino IDE.
  6. Now all you have to do is download the ZIMODEM software, then open the main “zimodem.ino” file in the IDE (the other files will open in different tabs, automatically), and build and load it to the ESP8266.

UPDATE: I did not need step 4 when I recreated these steps on my Mac, so maybe they are not even needed on the PC side these days.

These steps worked for me, but I want to go back through them (as well as finding Mac instructions and Linux if someone can assist me with that) and add photos and more details.

FTP, IRC, TELNET and more! Oh my!

ZIMODEM was created for Commodore computers, and has some special features in it for translating normal ASCII to Commodore’s PETASCII. It also comes with steps on how to use it with a Commodore from BASIC (with some assembly language routines used for high-speed reading and writing to the modem – sound familiar?). They have source code for various internet utilities such as:

  • WGET (get a file from a website)
  • FTP
  • IRC (chat)
  • TELNETD (for connecting to the Commodore remotely and using BASIC over the Internet)
  • WEATHER (a two player network game from the Commodore PET days)
  • …and others.

With DriveWire on the CoCo, some of this exists but only for OS-9. It is my hope that we can easily port these BASIC programs (and even replicate the assembly language routines) over to the CoCo and do the same thing.

More to come…

Sir Sound 2018 update: Now with WiFi and Bluetooth???

Last year, Sub-Etha Software “announced” the Sir Sound, a sound add-on for the Radio Shack Color Computer that would plug in to the Serial I/O (i.e. printer or bitbanger) port. The prototype looks like this:

Prototype “Sir Sound” sound module for the CoCo (or anything with a serial port, actually).

The idea was, by making this device “smart”, you could send simple, small commands to it and it would take care of the actual music playing, freeing up CPU time for the program. Since the device was “smart,” firmware could also be expanded with new features added.

The plans will be available for anyone who wants to build their own, and the source code will be posted to my Github repository. For someone like myself, with little or no hardware skills, you will be able to build this just by plugging wires into a breadboard (like the prototype). It’s not pretty, but it’s cheap and easy. And fun!

Various Sir Sound options…

I have contemplated designing a custom board for this, which would have a handful of chips and parts on it as well as a serial port and USB plug. Basically, it would be a board version of the prototype. The cost on this would be pretty low, but since I am not a hardware guy, I likely wouldn’t want to be the one soldering all the parts together.

Another option would be to just make an Arduino Shield that plugs in to a cheap Arduino UNO clone. You can get a good-quality Arduino for around $6, shipped from the USA by resellers on e-Bay. This could make the cost of the “Sir Sound” portion lower, though you’d still need an Arduino. You can buy a fully-made Arduino for less than the parts to build a clone, so this seems like a good way to reduce costs.

So which is better: Full board with everything, or add-on Shield for an Arduino?

I am not sure if the cost of the Arduino header pins is more expensive than the few chips it takes to just make the Arduino circuitry on a standalone board ;-) But, for folks who already have an Arduino, the add-on Shield is a great way to re-use existing hardware (and you can then use it for other projects when you are not hooked up to the CoCo). And, even for for those who don’t already have an Arduino, it might still be cheaper than the fully custom solution.

Sound + WiFi?

But what if it could do more than just sound?

Recently, I started playing with the ESP8266 WiFi chip. This device has a built in networking stack and WiFi hardware. It also has RAM and flash storage, and you can load it with custom firmware. This module is cheap! I ordered a “developer kit” with a USB port for less than $9 from Amazon.

An ESP8266 development board, available for under $9 from Amazon. (And much less from China!)

See those pins on the bottom? These developer modules make all the I/O lines available, it would be possible to make a small board with the sound chip and serial port on it that this plugs in to. This could give you sound and WiFi!

For the bitbanger serial port, baud rate on WiFi and Bluetooth would be limited to a slower speed, but if could also be plugged up to an RS232 Pak for high speed networking.

And, this looks like it would be cheaper than using an Arduino! More features for less money?

And, for a few bucks more, there is a module that adds Bluetooth as well, giving you sound, WiFi and bluetooth!

To be continue…

Let’s just say there are a few prototypes in the works right now… And they are all very cheap.

More to come…