I never shared this test program here, it seems, but you can find the full article over on Vintage is the New Old. This program will work on a CoCo 2 (or emulator) that has the later 6847T1 VDG chip. If the CoCo 2 has a slash in the zero on the screen, that’s the T1 chip.

0 REM 6847T1 VDG &HFF22
0 ' BIT 0) 01
1 ' BIT 1) 02
2 ' BIT 2) 04
3 ' BIT 3) 08 BG COLOR
4 ' BIT 4) 10 LOWERCASE
5 ' BIT 5) 20 REVERSE
6 ' BIT 6) 40 BORDER=BG
7 ' BIT 7) 80
10 CLS:PRINT "6847T1 VDG Demo"
20 L=&HFF22

100 ' NORMAL
110 PRINT "Normal"
120 REM
130 GOSUB 1000
140 PRINT "Normal + Border"
150 POKE L,PEEK(L) OR 2^6
160 GOSUB 1000
170 PRINT "Normal + Border + LC"
180 POKE L,PEEK(L) OR 2^6 OR 2^4
190 GOSUB 1000

200 ' REVERSE NORMAL
210 PRINT "Reverse Normal"
220 POKE L,PEEK(L) OR 2^5
230 GOSUB 1000
240 PRINT "Reverse Normal + Border"
250 POKE L,PEEK(L) OR 2^5 OR 2^6
260 GOSUB 1000
270 PRINT "Reverse Normal + Border + LC"
280 POKE L,PEEK(L) OR 2^5 OR 2^6 OR 2^4
290 GOSUB 1000

300 ' ALT COLOR
310 PRINT "Alt Color"
320 POKE L,PEEK(L) OR 2^3
330 GOSUB 1000
340 PRINT "Alt Color + Border"
350 POKE L,PEEK(L) OR 2^3 OR 2^6
360 GOSUB 1000
370 PRINT "Alt Color + Border + LC"
380 POKE L,PEEK(L) OR 2^3 OR 2^6 OR 2^4
390 GOSUB 1000

400 ' REVERSE ALT COLOR
410 PRINT "Reverse Alt Color"
420 POKE L,PEEK(L) OR 2^5 OR 2^3
430 GOSUB 1000
440 PRINT "Reverse Alt Color + Border"
450 POKE L,PEEK(L) OR 2^5 OR 2^3 OR 2^6
460 GOSUB 1000
470 PRINT "Reverse Alt Color + Border + LC"
480 POKE L,PEEK(L) OR 2^5 OR 2^3 OR 2^6 OR 2^4
490 GOSUB 1000

999 GOTO 999

1000 ' INKEY
1010 IF INKEY$="" THEN 1000
1020 RETURN