600D Control Register Expander
Posted: Wed Jun 19, 2019 2:50 pm
Hi, while working on my Monitor ROM Menu code I had the idea that a couple extra control lines might be handy, so I whipped up a little adapter board. This board plugs into U72 and replaces the 74LS174 HEX flip-flop chip with a 74LS273 OCTAL chip, thereby giving two additional controllable lines.
These lines could be used as upper address line (like BK0 and BK1 are used for BASIC ROMS) for roms like the Monitor ROM, or character generator rom, allowing these to be under software control. All lines are brought out to a header, so you can also use it to tap into the existing control lines.
With this the 600D control lines would be:
0- 32/64 column mode
1- Color Enable
2- BK0
3- BK1
4- DAC Disable
5- User Defined (existing)
6- User Defined (expanded)
7- User Defined (expanded)
Here is the board:
Please excuse the render. The socket would be a header on the other side of the board....
Let me know if you're interested in something like this.
Steve
These lines could be used as upper address line (like BK0 and BK1 are used for BASIC ROMS) for roms like the Monitor ROM, or character generator rom, allowing these to be under software control. All lines are brought out to a header, so you can also use it to tap into the existing control lines.
With this the 600D control lines would be:
0- 32/64 column mode
1- Color Enable
2- BK0
3- BK1
4- DAC Disable
5- User Defined (existing)
6- User Defined (expanded)
7- User Defined (expanded)
Here is the board:
- OSI-CRX.jpg (146.55 KiB) Viewed 5802 times
Let me know if you're interested in something like this.
Steve