Daryl's 6502 SBC help

[jds]

The first board I designed had a PLCC44 footprint, my PCB software didn't have that at the time so I made my own, but mis-numbered the pins down one side (might have been more I don't recall), and even that was repairable without too much mess. I guess you'd need to go very wrong to have to scrap a board when working with two layer designs, most things are fixable by cutting traces and soldering in small patch wires, as long as you don't need to add extra components.

[8BIT]

Hi all,

I just caught up on this thread. I had a guy from Germany ask about SBC-2 boards a few weeks ago. If there is enough interest, i.e. at least 10 boards, then I could do a bulk purchase of the SBC-2.5 boards. I can provide a price breakdown based on # of boards requested if you are interested.

Daryl

[RichCini]

Hi --

Just to add, I have a bunch of blank 6502 boards available -- it's a derivative of Daryl's original v2.5 board but includes a bunch of nifty adds including video output (also adapted based on Daryl's video circuit), a joystick and Serial IEC. Info on the board itself is on my Web site (http://www.classiccmp.org/cini/6502proj.htm).

Rich

[beholder]

Hi Everybody.

Ok, I finally found the issue!
I had the wrong 7400 datasheet and was connecting the 7400 pins all wrong
But on top of that I did a horrible wire wrap job (my first time doing it) and I also found some wires where insulation broke off and was touching other wires.

I did a much better job this time and should have it up n running soon
It was quite annoying to take all wirewrap out and redo, but it was worthy!

Thanks!

[GARTHWILSON]

I have a wire-wrap page at http://wilsonminesco.com/6502primer/WireWrap.html .

Good luck and progress.

[beholder]

Good news, SBC wirewrapping is done and it works! Yay!
6522 is outputting the correct value.

Thanks Garth, I did read your article

Next step, test the 6551 and see if I can connect to my computer through serial

Thanks for all the help!

[beholder]

Hi Everyone.

Board is fully assembled, added 2nd VIA and wrote a simple program that confirms that 6502, clock, reset, 6522 (1 & 2), ROM and RAM works!!! Yay!
Now... as for my 6551 I tried connecting it to my computer and no luck so far.

I burned my EEPROM with Daryl's SBC-2 os, connected a ftdi (ft232rl) to usb on my mac.
my ftdi breakout board looks just like this one: https://www.sparkfun.com/products/9716
Seems to be a legit ftdi chip and I also have the driver installed on my mac.

I tried establishing a connection using Mac's terminal screen, but no sign of life.
I can see my ftdi breakout board tx LED lighting when I type my keyboard, but no reply.
I used 9600 baud rate... is that the correct baud rate?

So Im not sure if my crystal is working either. I also bought a mica 22pf capacitor, which I wonder if that's the problem.
Here's my ACIA crystal n 22pf capacitor that's on my board:
http://www.mouser.com/ProductDetail/ECS ... t4Qg%3D%3D
http://www.jameco.com/z/DM220-22pf-500- ... 16037.html

I tried probing the 6551 pin 6 and 7 with my oscilloscope but on pin 6 I see nothing and on pin 7 some weird erratic signal.
Can I probe the 6551 crystal? Would I be able to see the 1.8432Mhz wave?
I just bought an oscilloscope and Im still learning how to use it
When I probe the 1Mhz can oscillator I can clearly see the square wave.

I have my 6551 connected to the ftdi breakout board like in this schematic:
http://www.grappendorf.net/projects/650 ... world.html

Only difference is that I have the ftdi 5v and gnd supplying the power for the sbc.
The sbc powers up fine. I checked and it's not an issue.

/CTS, /DCD and /DSR are grounded. 6551 Tx and Rx connects to the FTDI Rx and Tx. the rest are left unconnected.

I was wondering if I'm doing something wrong that you guys can help me with the above description.
Thanks in advance for any suggestion!

[beholder]

WDC 65c51 datasheet schematic says I need to use a 30pf capacitor and 1Mohm resistor...
I dont have the resistor. Is that needed? Also my capacitor is 22pf.

[8BIT]

beholder wrote:

I used 9600 baud rate... is that the correct baud rate?

The default SBC2OS used 19200,n,8,1

Also, just to be sure, FTDI TXO goes to the 6551 RX and FTDI RXI goes to 6551 TX.

On power up, the SBC should send a small greeting. You could monitor the 6551 TX pin to see if its leaving?

Daryl

[beholder]

Tried connecting using 19200 but nothing.
The 6551 Rx and TX are always high... not sure if thats okay.

I did add a 1M ohm resistor between pin 6 and 7 and then I can see a 1.8432Mhz square wave on my osciloscope.
However the wave is on pin 7, pin 6 is low.

Im gonna check if my ROM has anything weird.
Thanks

[GARTHWILSON]

beholder wrote:

Rx and TX are always high... not sure if thats okay.

It just means no data is going across.

Quote:

I did add a 1M ohm resistor between pin 6 and 7 and then I can see a 1.8432Mhz square wave on my osciloscope.
However the wave is on pin 7, pin 6 is low.

Pin 7 will have a square wave, but not pin 6. The 1M resistor might be needed on some manufacturers' 65(c)51's for biasing, but I'm not using it on Rockwell's or CMD's, and they work fine without it.

[8BIT]

It could be in the 6551 chip selects... monitor the /7F7x output (pin 7) of the 74LS138 for low pulses and verify its also reaching pin 3 of the 6551. Be sure also pin 2 of the 6551 is connected to +5v.

After Reset, it should be trying to send:

65C02 Monitor v5.1 (5-30-05) Ready
with Enhanced Basic Interpreter (c) Lee Davison
(Press ? for help)
>

So you should see several pulses at pin 3 of the 6551 each time you press and release the reset button.

Daryl

[beholder]

Hi everyone.
Thanks for all the tips. I'm getting closer at solving this issue!
So crystal is working fine now that I have the 1Mohm resistor.
I burned the eeprom again and check its content and it looks fine as well.

I plug some LEDs to the address bus and gave the sbc a slow clock to check what it's doing.
I can see it's running a loop. Im going to write down the address and compare with the eeprom content.

After testing all address decoding pins I found that 7F7x output is always HIGH, so its not activating the 6551.
The 74hc30 IO select (pin 8 ) is blinking, so my guess is that might be a problem on the 138. (thanks for pointing that out Daryl)

Will do some more testing later today.
Thanks!

[8BIT]

Check all of the inputs in the 74HC138, pins 1-6. If something is wrong there, then /7F7X will not go low.

Daryl

[beholder]

I checked all pins on the 138 and I noticed that pin 2 (A5) doesnt light up.
Its not a bad connection... A5 on the address bus is never HIGH during the loop

I'll write a simple program to test if the address decode logic can trigger the 6551

Just out of curiosity... on the sbcOs rom file, I see $92 on address 7F0D
Is that an opcode? Just wondering what it does.
Im new to 6502 assembly and I hope I'll learn more once my sbc works.
Thanks!