6560 Maximum Memory

[DrVeryEvil]

I've been pondering the VIC I chip and the memory configuration on the VIC 20. The 6560 can access 16K of memory according to the datasheet and is indicated by the address bus of the VIC I, having 14 address lines. The 6560 can access the first 8K of memory, if the VIC20 has internal 3K. Then there is 4K for the character ROM. The color memory has 4-bit data, connected to D8 - D11 and is mapped to $9400 - $97FF and its location is dependent on the video matrix location. The control registers are from $9000 - $900F and can only be accessed during Phase2 = 1. I guess my question is, can the 6560 make use of 8-bit memory from $9800 - $9FFF. It looks like the color memory is totally controlled by the 6560 and is fixed, so I don't think it can be used for color memory. I additional memory all has to be connected to the 6560 to be accessible for video. In theory, can the 6560 access another 4K of 8-bit RAM above the character ROM? How much of this memory is usable by the 6560?

[pixel]

I've been pondering the VIC I chip and the memory configuration on the VIC 20. The 6560 can access 16K of memory according to the datasheet and is indicated by the address bus of the VIC I, having 14 address lines. The 6560 can access the first 8K of memory, if the VIC20 has internal 3K. Then there is 4K for the character ROM. The color memory has 4-bit data, connected to D8 - D11 and is mapped to $9400 - $97FF and its location is dependent on the video matrix location. The control registers are from $9000 - $900F and can only be accessed during Phase2 = 1. I guess my question is, can the 6560 make use of 8-bit memory from $9800 - $9FFF. It looks like the color memory is totally controlled by the 6560 and is fixed, so I don't think it can be used for color memory. I additional memory all has to be connected to the 6560 to be accessible for video. In theory, can the 6560 access another 4K of 8-bit RAM above the character ROM? How much of this memory is usable by the 6560?

Unfortunately the VIC cannot access RAM which is not internal unless you grab a soldering iron AFAIK.

[DrVeryEvil]

You are correct Pixel.

The VIC 20 Programmer's Manual lists this.

According to this, if I were to wire memory directly to the 6560, I could address memory above $9000. I don't think I'd be able to use any of it before the end of color memory, but it might be good for a small bitmap. I don't know how color memory would react to having 8 bit memory connected alongside the 4 bit color memory. They do have different data busses, but the same addresses, so that probably won't work. I'm thinking about building a board with a 6560 as a video card that plugs into the 6560 socket that would have more capabilities than the standard VIC 20 circuit.

The 3 bits labelled for the Character ROM only uses half of all the memory location options. $9000 holds the VIC registers and $9110-$9120 holds the VIA's. $9400 is color memory. $9800 and $9c00 wouldn't be enough for the 6560 to do anything with. The datasheet doesn't really say anything about a maximum memory configuration, just the minimum. Could this 2K of memory be used as another bank of color memory?

[DrVeryEvil]

A quick tip, all the data and address line are accessible from the character ROM chip.

[srowe]

A quick tip, all the data and address line are accessible from the character ROM chip.

Back in the 80's I made an internal 3K expansion module that fitted into the socket

https://www.sleepingelephant.com/ipw-we ... php?t=7016

[mythic66]

I'm thinking about building a board with a 6560 as a video card that plugs into the 6560 socket that would have more capabilities than the standard VIC 20 circuit.

I think this is the best way. I'm finishing a little project on the CPU side, and I made a daughterboard which give me access to everything the CPU see, so same thing for the 6560.

[DrVeryEvil]

I'm curious what you have there?

[mythic66]

I'm curious what you have there?

still cooking atm, i'll start a thread when it will be ready , to not to highjack the thread.