I've been struggling off and on for the last few days.

I'm not near my board at the moment so I can't post a pic or schematics...but I can if they are needed.

Anyway, I'm having three different issues. The example I'm following is here:

http://www.grappendorf.net/projects/6502-home-computer/acia-serial-interface-hello-world.html

I've built that circuit for the most part. The differences are:

1) I'm using a 65C02 instead of the NMOS version.
2) I only have 8K EEPROMS and not 32K
3) I have a 3k3 pull-up for RESET with a push-button to GND.
4) I have a 3.579545 MHz clock running through a 74'4040 counter to get a 1.79...MHz clock.

Here are the issues I'm having:

1) Power. The entire breadboard is only using 11 mA. I have the 65C02, a ripple counter, a hex inverter, ROM and ACIA and I'm only pulling 11mA? Sometimes it drops to 9mA. Something is wrong. I am using a bench power supply at 5v and 1A max. Each IC has a .1uF cap on VCC that is as close as I can get it. Since this is a large breadboard, I have large 1000uF electrolytic caps all over the board in hopes of providing enough power. But nothing seems to be using it. I have an LED on the opposite end of the board that lights up just fine and he's pulling an additional 12 mA. When the LED is plugged in, I pull 23 mA. No LED = 11 mA. Oh, each IC will read 4.9V on the high end and 4.2V on the low end.

2) ACIA clock. I have the 1.8xxx MHz crystal tied to pins 6/7 of the 65C51. I put a 22pF cap from pin 7 to GND. Sometimes it works, most of the time it doesn't. I then put another 22pF cap on pin 6 to GND and then it will work for a little while. Scope shows what I expect 1.8xxx MHz. If I wiggle the crystal around for a while, it will sometimes start clocking correctly. But 80% of the time, the scope just shows 5V straight line (well, a little ripple but mostly straight...especially with averaging turned on).

3) Serial data. The little program on the webpage I listed just performs a simple "hello world" over the serial port. Sometimes, and I mean just sometimes, I will get random garbage come over the terminal. But it's never "hello world". For serial communication, I am using this device: https://www.parallax.com/product/32201. I am connecting the 65C51's TX pin to the RX of the PropPlug and the RX to the TX of the PropPlug. GND to GND. The PropPlug also has a "RESET" pin for rebooting the mCU but I'm not using that.


Here is what I've done to try and solve my issues (not a complete list!):

1) Large capacitors all over the board to help distribute power. I've seen the board pull as high as 63 mA but it usually drops to 11 quickly. I've put large caps near each IC in hopes that each would have their own power reserve (in addition to the decoupling caps mentioned above).

2) Plugged my frequency generator into pin 7 of the 65C51 with the exact frequency dialed in.

3) Made sure each wire was the same length for any bus. As best as I could. Checked, re-checked and re-checked 5 more times on my wiring. Since I am only using 8K ROM, I left A14 and A13 floating. (I've also grounded them at one point).

4) Lowered the system clock down to 3.579545 / 4 = < 1 MHz clock.


The schematics are almost exactly the same as the URL above. I can post some pictures later this evening. But I thought I would ask for guidance while it was still fresh in my mind.

Thanks for any help!

** EDIT **

BTW, I ordered a couple 32K EEPROM's (28C256) and 3 DS1813's.

Also, I just realized the "SBC-2 v2.5" http://sbc.rictor.org/info2.html is pretty much exactly the computer I want to build. Stupid me! The only difference is that I want to integrate some AY audio chips and a TMS9918 eventually. I will look over that design too. Regardless, I'd like to know what I did wrong in my existing setup too.

_________________
Cat; the other white meat.

Please post the schematics. It will make it a lot easier to help you out with this.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

Unfortunately, I haven't drawn up any yet. ;-/

But this is 99% of what I have built.

http://www.grappendorf.net/images/projects/6502-home-computer/homecomputer-6502-v5-acia-schematic.png

The difference is that I don't have an AT28C256. What I have instead is an 8K version (AT28C64B) that doesn't have A14 or A15.

Everything else is identical (that I can tell).

Thanks.

** EDIT **

Also, I took this code and typed it by hand in my EEPROM programmer:

_________________
Cat; the other white meat.

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Good point. I originally had a 555 timer reset circuit but I thought it might be overkill for a breadboard. Especially when I knew I would be ordering a DS1813 soon. I may solder up a little 555 timer on some perf board just for this purpose. I was also following the L-Star SBC that I have which seems to do OK with a simple pull-up and mechanical switch. However, it does sometimes need to be reset twice to boot.




Each IC's VCC pin reads between 4.2v and 4.9v with 4.6v or so being the norm. GND reads a few mV (basically 0).




So, you're saying put the 22pF cap from 6 to GND (instead of pin 7) and tie a 1M resistor between the two? What would the resistor be for? The brand of 65c51 I have is WDC. Do they normally need that?




Ah. I will try that too. The large breadboard I have is 3x3 boards on a cookie sheet. That's why I was thinking power distribution would be bad. At the very least, I will put a large cap at the top/middle/bottom.



My target frequency is going to be 1.79 MHz for the CPU. All driven from a 3.579545 MHz crystal. That's mainly because the AY chips I want to use seem to like 1.79 MHz or even 3.579545 MHz. So I hope to provide a jumper to let me choose. But I was wondering if even 1.79 MHz was a little too fast for a breadboard. Even with short traces.



I'm pretty sure the 8K EEPROM programmed correctly. I pulled it out and loaded the data back in my computer and the numbers matched.

I will, however, triple check the wiring to make sure I didn't make any false assumptions.

Thanks!

_________________
Cat; the other white meat.

Do you have any confidence that a program is running? Can you measure activity on Sync, on RnW, on CS lines, on address lines?

Complete confidence, no. Unfortunately, I don't have a logic analyzer.

However, when I put my scope on certain address pins, I see square waves of different frequencies. In fact, it's like I'm seeing two different waves on the same pin. My assumption is because the I/O and ROM are getting switched on/off.

What I can try doing is recording the frequencies of all address pins on each IC. Maybe that might help clue me in.

Any suggestions on confirming if the code is running?

I wonder if I should remove the ACIA and replace it with a VIA to see if I can blink some LED's. But the ACIA seemed simple enough to get going...in theory at least.

_________________
Cat; the other white meat.

I'd recommend putting something trivial into the ROM so you can get more evidence from the address pins. For example, a loop containing 256 NOPs or 128 LDA #$A9 instructions. Or a tight loop containing just a JSR, so you can monitor page one addresses and the read-write lines doing interesting things.

That's a good idea.

I actually did that before I wired up the ROM and ACIA. I hard-wired the CPU's databus to NOP and watched the address pins. That worked.

However, I need to do the same thing from ROM memory.

_________________
Cat; the other white meat.

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Thanks again for the reply. Hopefully, I will get to work on it some more tonight.

Regarding the breadboard...

I know PCB's are cheap these days...but I can't justify spending $20-$40/pop for each mistake. I've seriously thought about getting some wire-wrap equipment. But that also seems a little expensive. So I mostly have to go with what I already have in stock.

That being said, I have tons of these little proto-boards and sockets. I'm thinking about soldering a small board with my breadboard wire for each IC and make them "stackable". I have tons of the 8 pin "Arduino" style female headers. Doing that, I can make the wires really short and they are soldered. So each module could have the data bus and address bus in the same spot for RAM/ROM/whatever. And I could then put control buses in a different place. So the amount of arc'd wires should be drastically reduced.

I'm just not looking forward to soldering hundreds of wires. lol

Ugh...the pain of prototyping.

_________________
Cat; the other white meat.

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

A circuit diagram made by you looking at your circuit as it is now is definitely needed as others have said - even if hand drawn and scanned in.
Also, it may be worth single cycling the circuit. I.e. instead of the entire circuit running at full speed, replace the PHI2 crystal with the following circuit:

The above is from Garth's website and is the fifth image down on this page: http://wilsonminesco.com/6502primer/ClkGen.html
What it does is generate a single 1uS pulse (a clock cycle) per click of a button. You can then use your oscilloscope to measure the buses/signal lines as needed to see if you are getting what is supposed to be there. I.e., the reset vector after reset, etc..

The other possibility is to build a NOP generator, a design for which is posted somewhere around here. That will cycle through all the addresses and prove that the 65C02 is working.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

(I believe cbmeeks already did exactly that - see the message after the one you quoted)