6502 CPU board for the RC2014

[Elminster]

bluesky6 wrote:

If you are just running a basic program loader or a Monitor, you can go as high as 62KB of RAM minus the i/o space.

If you want to include a variant of BASIC plus the Monitor or just BIOS, you might be able to get 56KB of RAM. Some variants of MS BASIC build to 8KB. I found that with EhBASIC, you'll need more ROM space e.g. 12KB if you include a monitor.

I was thinking about getting the Pro board(just because it isn't much more) and the bare bones (the 5 mini PCBs). The price for buying the ram, rom, and serial separately was more than buying the 5, even if I don't need z80 and clock.

Have you played with the advanced modules yet?

[Michael]

bluesky6 wrote:

If you are just running a basic program loader or a Monitor, you can go as high as 62KB of RAM minus the i/o space.

If you want to include a variant of BASIC plus the Monitor or just BIOS, you might be able to get 56KB of RAM. Some variants of MS BASIC build to 8KB. I found that with EhBASIC, you'll need more ROM space e.g. 12KB if you include a monitor.

I've used a build of Grant Searle's modified OSI BASIC that runs in $E000..$FEFF with a monitor in page $FF and I/O mapped into page $DF which does indeed provide almost 56K of RAM.

[bluesky6]

Elminster wrote:

Have you played with the advanced modules yet?

What do you mean by "advanced modules"?

In my blog I covered the use of the 64KB RAM and Pageable ROM modules with the 6502 CPU Board.

[Elminster]

Sorry I meant 'Enhanced' not 'advanced', as in Enhanced bus. My understanding is to make full use of the 64k boards etc you need the enhanced bus extra row of pins for the additional signals. I think you said you didn't have the enhanced backplane but the original one? Not sure what the extra pins give you.

BTW is that a 16 or 25V Electrolytic Capacitor on your 6502 board? Looks like a good project for me to kick off my 6502 investigations on.

[bluesky6]

Elminster wrote:

Sorry I meant 'Enhanced' not 'advanced', as in Enhanced bus. My understanding is to make full use of the 64k boards etc you need the enhanced bus extra row of pins for the additional signals. I think you said you didn't have the enhanced backplane but the original one? Not sure what the extra pins give you.

I'm not sure either

The additional pins bring out more of the Z80-specific signals. What is applicable to the 6502 world might be NMI and Wait (RDY).

The other lines are "upper" data lines but IMHO not too useful without additional address lines e.g. other than the Z8002, most 16-bit processors (680xx, 8086 etc) require more than 16 address lines.

Elminster wrote:

BTW is that a 16 or 25V Electrolytic Capacitor on your 6502 board? Looks like a good project for me to kick off my 6502 investigations on.

That cap is for the reset circuit running at 5V max so a 16V will do. The key is to have a small one as the one that I have gets in the way of the adjacent board.

[Elminster]

Great thanks.

I plan to get a small run of your board this month, and then buy all the other components and RC2014 boards next month (after pay day, due to cash flow).

Keep up the articles on the blog! Also reading the MY6502 blog but that one doesn't have a nice board like yours.

[Michael]

bluesky6 (Ben):

Have you considered adding jumpers on the '688 'Q' inputs to allow the user to select the I/O page? Probably would need pull-ups or pull-downs too, yes, no?

Cheerful regards, Mike

[bluesky6]

Michael wrote:

bluesky6 (Ben):

Have you considered adding jumpers on the '688 'Q' inputs to allow the user to select the I/O page? Probably would need pull-ups or pull-downs too, yes, no?

Cheerful regards, Mike

I have considered making the I/O page selectable but it would have made the PCB a little more complicated.

The other option is to go back to the RC2014 basics i.e. the I/O page selector on its own board.

You won't need pull ups or downs: tie the inputs to Vcc or Gnd.

[commodorejohn]

Hmm, that's not a bad idea. Make it a little standoff from the main board and you can just wire it up for any page you want.

(I've always figured either the page immediately after the stack or immediately before the ROM would be best, as that way you get the most contiguous general-purpose RAM.)

[bluesky6]

commodorejohn wrote:

(Also, have you run this at higher clock rates? Any idea what the highest stable frequency for it is?)

So I got around to mucking around with the Western Design Center W65C02 which is rated at 14MHz.

Guess what...

It didn't work. Well, the monitor/debugger started out and then printed rubbish.

After some experimentation that included hard wiring BE (pin 36) to VCC, I found out that the RAM chip was too fast.

Yep, a 55ns Alliance 32KB static RAM chip was too fast for a W65C02 running at 4MHz. I had to use a slower 70ns Cypress RAM chip.

Note that I had successfully tested everything from Rockwell/Synertek NMOS chips, Rockwell/CMD CMOS chips (at the rated frequency) with the 55ns SRAM.

In case you were wondering if that SRAM chip was bad. It wasn't. I have 5 of them and none of them would work reliably with the W65C02. And I don't think I've a bad W65C02 either. I have 2 and they both had the same issue.

Go figure.

Anyway, I'm currently running the same W65C02 at 7.3728MHz. And yes, it's fast.

The good news is that the 70ns 32KB RAM is available from Jameco (#82472) or Mouser (727-CY62256NLL70PXC).

[GARTHWILSON]

I'm sure there's no way it could be too fast. More likely is that it couldn't pull up high enough for the WDC processor to recognize a valid logic '1'.

[commodorejohn]

Hah, interesting. I have piles of 32KB SRAMs but they're all 15-20ns cache chips from 386/486 motherboards. Guess we'll see how that all shakes out.

[GARTHWILSON]

Plenty of customers have used my 4Mx8 10ns 5V SRAM modules with the W65C816S, with no problems reported.

[Michael]

bluesky6 (Ben);

Which RAM board are you using, please? Is it the standard 32K board?

[floobydust]

bluesky6 wrote:

commodorejohn wrote:

(Also, have you run this at higher clock rates? Any idea what the highest stable frequency for it is?)

So I got around to mucking around with the Western Design Center W65C02 which is rated at 14MHz.

Guess what...

It didn't work. Well, the monitor/debugger started out and then printed rubbish.

After some experimentation that included hard wiring BE (pin 36) to VCC, I found out that the RAM chip was too fast.

Yep, a 55ns Alliance 32KB static RAM chip was too fast for a W65C02 running at 4MHz. I had to use a slower 70ns Cypress RAM chip.

Note that I had successfully tested everything from Rockwell/Synertek NMOS chips, Rockwell/CMD CMOS chips (at the rated frequency) with the 55ns SRAM.

In case you were wondering if that SRAM chip was bad. It wasn't. I have 5 of them and none of them would work reliably with the W65C02. And I don't think I've a bad W65C02 either. I have 2 and they both had the same issue.

Go figure.

Anyway, I'm currently running the same W65C02 at 7.3728MHz. And yes, it's fast.

The good news is that the 70ns 32KB RAM is available from Jameco (#82472) or Mouser (727-CY62256NLL70PXC).

I've also had some odd issues with the Alliance 32KB SRAM chips. I have four of them... one has a problem and won't run with my board set, the other 3 are fine. It passes a RAM test fine but it simply doesn't work. The problem is with Page $03, as the problem only appeared when I started using that page for holding vectors and configuration data.

There's a chance you're seeing more noise with the WDC chip (I recall seeing a post here a while ago, but forgot who initially posted it). You might want to try adding some additional bypass caps on the CPU and the memory chips. I'm currently running at 10MHz with 70ns memory (Alliance 32KB and Atmel 28C256), but I added additional bypass caps to all of the chips on the CPU board.