LOWERCASE
COLOR COMPUTER 1,2, DRAGON 32,64, MC-10
The original MC6847 VDG used in the Color Computer 1, 2, Dragon 32, 64, and MC-10 are well known for using uppercase only text, and representing lowercase using inverse-colored versions of the uppercase characters.
However, the VDG supports external character ROM capability, which led to Green Mountain Micro offering an add-on board called the Lower Kit which added multiple font options including lowercase.
The FPGA-based CoCoVGA offers a similar custom font capability to the Lowerkit and can be used in the Dragons and MC-10 as well.
COLOR COMPUTER 2B
The MC6847T1 upgrade to the Video Display Generator added lowercase characters with descenders to the font bitmaps in ROM.
For backwards combatibility, the VDG starts up in all uppercase mode.
To switch into lowercase:
POKE &H0167, &H39 POKE &HFF22,(PEEK(&HFF22)OR16)
The POKE &H0167,&H39 redirects the RVEC3 console out from resetting the video mode back to all uppercase.
The POKE &HFF22,(PEEK(&HFF22)OR16) flips bit 4 of the PIA1 control register which controls the VDG mode.
You can use OR 32 to switch the video to INVERSE mode.
You can use OR 64 to switch the border color to green.
A version of the CoCoVGA for the MC6847T1 exists to bring the rest of the CoCoVGA features to the CoCo2B as well.
COLOR COMPUTER 3
The GIME chip in the Color Computer 3 includes the MC6847T1 VDG font for backwards compatibility.
The 32×16 hardware text mode also defaults to all uppercase for backwards compatibility.
To switch the CoCo3 hardware text screen into lowercase mode:
POKE &H95C9,&H7F POKE &HFF22,&H10
This tip was shared by Bob Rosen in Rainbow January 1987 page 146.
The POKE &H95C9,&H7F changes the RAM copy of the Extended Color BASIC ROM to stop masking off certain bits of the VDG control register in its console out.
The POKE &HFF22,&H10 is a shorthand way of forcing just bit 4 on and all others off in the PIA1 VDG control register.
The same POKE , PEEK OR 16 used on the CoCo2B will also work.
VDG REFERENCE
Memory Mapped Address $FF22 (PIA1 Port B Control) selects some VDG settings
| BIT | PURPOSE |
|---|---|
| 7 | VDG Alpha/Graphics (A/G) pin |
| 6 | VDG Graphic Mode 2 (GM2) pin, T1 border color switch |
| 5 | VDG Graphic Mode 1 (GM1) pin, T1 inverse mode switch |
| 4 | VDG Graphic Mode 0 (GM0) pin, T1 lowercase mode switch |
| 3 | VDG Color Set Select (CSS) pin |
| 2 | RAM Size In |
| 1 | One Bit Sound Output |
| 0 | RS-232 IN |
RTS
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