6502.org

Hi all,
Newbie here, building an RC6502 Apple 1 SBC using an Issue H board.

Soldering is complete and to speed things up, I got a TL866 II Plus to burn the EEPROM which is an AT28C64XF-25PI (from EBay)
TL866 is new out of box and I reflashed the firmware in it. The device drop-down doesn't show an exact match but tried various flavours
and no joy.

I suspect the 28C64 is a 250mS part and I wonder if it is too slow???

Any ideas??
Cheers
Reg

Welcome, Reg.

250ms would indeed be too slow but I think you mean 250 ns, which should be fine. (Your clock rate is only 1 MHz, am I right?)

It might be a mistake to focus your troubleshooting on the EEROM. Perhaps that chip is misprogrammed, but it's also possible your project has a problem elsewhere.

In order to assist most effectively we will need more information, starting with photos (which you're allowed to attach to your post). And the CPU -- is it really "RC6502" or is it actually R65C02?

A schematic will also be helpful; also the symptoms you've observed so far. IOW, how does the system behave? Cheers,

Jeff

Hi Reg,

Double check your jumper settings before you try anything else... A14 Select and A15 Select need to be un-jumpered to use a 28C64, and ROM_EN needs to short pins 1 and 2 to enable the ROM chip. The way the board is laid out can make this non-obvious at first.

Make sure your ROM chip is good by reading it back and comparing the dump file with the file you wrote. I seem to remember that the EEPROM programmer you have has a "detection mode," so you can tell it to look for a specific chip (in this case, 28C64) to make sure you bought the part you think you did.

If that doesn't uncover the problem, give more details... what specific CPU are you using, what clock speed, etc. I found the SBC version to be a bit fussy to get working, but I did eventually find success. (My modular backplane version is zooming along at 8Mhz with a modern WDC 65c02.

Edit: Hey, rereading your first post, I think maybe I misinterpreted your question. You're having trouble getting the ROM to work with the programmer, not with the SBC, is that right? In that case I'd suggest abandoning the manufactured software and switching to "MiniPro:" https://gitlab.com/DavidGriffith/minipro/. I run it on an old ThinkPad with ubuntu; there's also a MacOS version. Not sure if there's one for Windows.

Hi Dr. Jeff
Thanks, that was quick off the mark. Typical of me to slip a quick '000 there

I am building the SBC off the github/tebl and will be using the 8k .bin file from there (when I can burn it).
Have done basic post-soldering tests and all chips except 28C64 are socketed but I have NOT turned on the power.
I am trying now to program the EEPROM in the TL866. Never done this before and it is a new toy

TL866 is from XGecu and the supported devices list from their site (28-pin dil only) is :-
AT28C64 AT28C64B AT28C64B(Non-Standard) AT28C64E AT28C64F
I have tried several of the above to no avail. I must admit I cannot find much detail on the XF variant.
Just noticed there are "HC" variants (not tried) of the 28*** but mine is definitely a "C"

I have attached a bit of 6502 Pron for you.

Thanks
Reg

Hi Paganini,
Thanks. Yes, I am still trying to bet the .bin file onto the 28C64 using the TL866.

I will give that alternative software a whirl later on and get back. Manufacturer's software often lets these devices down.
Linux isn't a problem; use WIN for day-to-day but have a laptop and another box on Linux.

Cheers
Reg

Great! My database has an "AT28C64" entry, which I think should work with your chip. I'm not totally sure what "XF" means, however. The Atmel data sheet doesn't list an "F" suffix, and googling for your exact chip doesn't turn up much.

Edit: I also came across this blog post: http://stuffandnonsense.elephantandchicken.co.uk/?p=904 Hopefully, you have not been the victim of counterfeit parts, but if you have you might be able to get it working by trying some alternate model codes. I'd suggest getting some more ROMs from, e.g., Mouser. You can never have too many ROMs!

Have you tried the Catalyst CAT28C64 device on the programmer? I had a case with a AT28C16 where the programmer wouldn't work with the Atmel device but would with the Catalyst.

Maybe it's nothing, but the 74LS04 looks a bit odd sitting in the socket. Might be worth checking to ensure all leads are inserted in the socket and that all chips are making good contact.

Beyond that, hopefully the software you're using to program the EEPROM can read the chip contents and allow you to view the buffer contents. This should allow you to get an idea of what's on the chip.

All,
Thanks ever so much for the help; it seems to be working now got into WozMon at least
Will elaborate more tomorrow when I have had a chance to test further.
Reg

All,
Thanks again everyone for the prompt attention.
It is indeed still working nicely this morning. I had the usual panic when plugging in because the jumpers were incorrect (who said non-obvious?). It is a good job it worked after that because my tools are limited to a soldering iron & DVM.

Have had a quick whirl on WozMon, Krusader & Basic.
Is there a sane way to get back to WozMon from the others?? (RST is fine though)
The MiniPro software worked perfectly using 28C64 although it is a long time since I have seriously used CmdLine (Solaris on Sun workstations mid-late '80s???). We get spoilt usin GUIs
MiniPro programmed and reported verified OK. I re-verified OK using Xgpro but noticed a "Pin Detect" error which may have been my original error.
Indeed, the 74LS04 was a bit twisted in the socket but making good contact. Not sure how I managed that.

Right, must dash and thank you all again
Cheers
Reg

Glad it's working! It's a good feeling when you fire it up and see what you're expecting, right?

It most certainly is

I am rather impulse driven and this project has taught me to take a bit more time. I saw the pcb on EBay and just went for it; ordering the
components from so many places, I had to create a spreadsheet to keep track. EBay is quick and easy but not ideal for the likes of this.
Fear of fake components probably got to me when trying to program the EEPROM so if there is another project will use Mouser or similar as
someone suggested.

I still have my BBC B (restored, working) which I bought in the '80s and was recently tempted to build the KIM-UNO from "oscarv" of this place
(thankfully came as a kit of components). Oscar's latest software emulates both the KIM-1 & Apple 1 and I was using that also on the "dongle" below.
It just seems logical to run WozMon etc on real hardware.

Reg

I have got the RC6502 working fine now; changed for an R65C02 and TaliForth2 is up and running too. I hand-built (vero - no pcb) a clock divider cct with an 8MHz oscillator in there. I initially built an SBC but have added a backplane with ROM/RAM card and clock cct.
It all runs fine at 4MHz and I am wondering what I might have to do to get it up to 8MHz?

It may well be the crazy wiring on my DIY divider board but I also have a random hotch-potch of 74.... series parts out of the parts bin.
Should I cnange them for HC. HCT???
As I said, CPU is a Rockwell R65C02 and the ROM, RAM, PIO should cope, yes??

The R65C02 will not run at 8MHz. They came in 2MHz and 4MHz parts. The most that you can run the 4MHz part at is about 5MHz. You will need a modern WDC W65C02 to go 8MHz (or more). Be aware that the W65C02 has a slightly different pin-out than the R65C02 and you will likely have to make some minor changes to your board to drop it in.

To run at 8MHz reliably you need your ROM and RAM to have access times of around 120ns or better. Your RAM looks to be 70ns so it should be fine. Your EEPROM looks to be 250ns. That may or may not work. The 6821 was designed to work in 1MHz or 2MHz systems. I am not sure how well it will keep up. I have had some luck with running peripheral chips at much higher speeds than rated (especially the 65C51), but it is hit and miss which devices will tolerate it and I'm not that familiar with the 6821.

My workbench computer originally had a Rockwell R65C02 rated for 4MHz, and it started having problems at a just hair over 7MHz, so I backed it off to 5MHz for some safety margin. I suspect the memory speed was the bottleneck.