SBC-1 1.1 Questions

asm_2750 · Post by **asm_2750** » Sun Oct 26, 2003 1:42 am

I got one question, it is possible to hookup the composite TV interface, and the keyboard interface on the same SBC?

8BIT · Post by **8BIT** » Sun Oct 26, 2003 9:37 pm

You can, if you want to modify the video design slightly.

The SBC 1 board has only 16 I/O bits (plus CA2 & CB2 as outputs).
This leaves enough for both the Video (phase 2 uses 15 outputs, 1 input) and two for the keyboard.

By moving two of the control pins from port B to CA2 & CB2, you can gain two pins on port B for the keyboard.

However, without multiplexing the pins, you won't have any left for other purposes.

Daryl

asm_2750 · Post by **asm_2750** » Tue Oct 28, 2003 6:35 am

Cool, also found a nice lot of brand new MOS 6502 and commodore 6522s on ebay hopefuly i win, that auction, now that i can make a generic atari, maybe i can read and play atari games :p, hopefuly make my own atari lynx 2 with less power consumption and sharper screen

nelbr · Post by **nelbr** » Tue Apr 19, 2005 7:39 pm

Hi Daryl,

Thank you for sharing your projects with us. I am a complete electronics newbie and I have learned a lot from studying your pages. I did have an Apple ][ long ago and at that time I knew 6502 programming pretty well.

I found your SBC1 project really cool, and if I ever have some spare time, I would like to give it a try. Not very likely at the moment though.

Anyway, I have a few questions that maybe you can answer:

In your SBC2, you changed the memory read-write logic decoding, in such a way that MRD does not depend on PHI2O. Is this ok? Because, by doing that on the SBC1 as well, you could save an entire 74LS00 that could be removed from the board.

Also, I was wondering why you use RAM space for I/O. Any specific reason for that? Because if we did the decoding logic as follow, couldn't we assign it to ROM space instead:

RAMSEL=A15
IOSEL=NAND(A8..A15)
ROMSEL=NAND(RAMSEL,IOSEL)

We would further save a NAND module on the first 74LS00 and have some very slight extra RAM

Anyway, congratulation on all this really cool stuff.

Nelson

8BIT · Post by **8BIT** » Tue Apr 19, 2005 11:26 pm

nelbr wrote:

In your SBC2, you changed the memory read-write logic decoding, in such a way that MRD does not depend on PHI2O. Is this ok? Because, by doing that on the SBC1 as well, you could save an entire 74LS00 that could be removed from the board.

Yes, you are correct. I found that the MRD did not need PH2. I have not gone back to the SBC-1 to incorporate any of my design changes. The SBC-1 was a fun first-try board but it really does lack the IO to make it useful. Unless you have a specific task you want it to do.

Quote:

Also, I was wondering why you use RAM space for I/O. Any specific reason for that? Because if we did the decoding logic as follow, couldn't we assign it to ROM space instead:

RAMSEL=A15
IOSEL=NAND(A8..A15)
ROMSEL=NAND(RAMSEL,IOSEL)

We would further save a NAND module on the first 74LS00 and have some very slight extra RAM

No. Your decoder would put the I/O @ $FFxx, which is where the reset, IRQ, NMI vectors are located. Thats why I took 256 bytes from RAM.

Thanks for checking out my site!!

Ask any more questions if you have them.

Daryl