Advice needed on SBC

[BigDumbDinosaur]

Floopy wrote:

BigDumbDinosaur wrote:

Floopy wrote:

I went and did a little more research. I finally have a (partial) schematic...

Can you please post your schematic in monochrome?

Sure? I updated a few things.

I'm not sure what to do with IRQ(not) and CS1 on the 6522?

Connect /IRQ on the 65C22 to /IRQ on the MPU. CS1 on the 65C22 can be connected to VCC. Be sure to pull up /SO on the 65C02 to VCC.

[Floopy]

BigDumbDinosaur wrote:

Connect /IRQ on the 65C22 to /IRQ on the MPU. CS1 on the 65C22 can be connected to VCC. Be sure to pull up /SO on the 65C02 to VCC.

Got it one there. I believe I have finished wiring up everything, I got the foot prints assigned. All I need to do is layout the PCB.

I tied all the unused logic pins to VCC.

This is the final document.

[BigDumbDinosaur]

Floopy wrote:

BigDumbDinosaur wrote:

Connect /IRQ on the 65C22 to /IRQ on the MPU. CS1 on the 65C22 can be connected to VCC. Be sure to pull up /SO on the 65C02 to VCC.

Got it one there. I believe I have finished wiring up everything, I got the foot prints assigned. All I need to do is layout the PCB.

I tied all the unused logic pins to VCC.

This is the final document.

R9 might be too high a value. For most LEDs, 20mA forward current is maximum. I run LEDs at about half that current, which would mean R9 would be 470 ohms.

While poking around the power supply, I suggest you place a low ESR electrolytic of 100 µF in parallel with C2. If you do this, also place a 1N4001 diode across pins 1 and 3 of the 7805, with the diode's anode connected to pin 3.

Which 65C22 are you going to use? Depending on that, you may need to pull /IRQ up to Vcc through a suitable resistor (3.3k).

Is U7 an inverter or a Schmitt trigger?

[Floopy]

They are schmitt inverters (7414). I'm using a W65C22N. Since it is open drain I do need a 3.3K resistor. I'll put a message on the board that says to opt it out in case I use a W65C22S.
http://www.westerndesigncenter.com/wdc/ ... df#page=31
Why do I need to put a capacitor in parallel with C2?

Updated schematic:

[BigDumbDinosaur]

Floopy wrote:

They are schmitt inverters (7414). I'm using a W65C22N. Since it is open drain I do need a 3.3K resistor. I'll put a message on the board that says to opt it out in case I use a W65C22S.

There's no problem with leaving the resistor connected with a W65C22S. If you attach other devices to /IRQ while using the 'C22S you will likely have to revamp the circuit.

Quote:

Why do I need to put a capacitor in parallel with C2?

You'll get better regulation. Current draw in digital circuits tends to be "spiky" in nature and momentary changes in loading can occur more rapidly than the regulator can respond. The capacitor helps to mask this characteristic.

Incidentally, the D3 protects the regulator if power is cut to the input side. When that happens, the output side of the regulator will be at a higher voltage than the input side until C10 discharges. That reverse potential could damage the regulator. As CMOS devices draw little current when quiescent, capacitor discharge could be slow, exposing the regulator to reverse potential for some time. The diode will produce an alternate discharge path for the capacitor and the reverse potential difference across the regulator will be limited to the forward drop of the diode.

[Floopy]

Okay, I took the comment out of the schematic. I'll start laying it all out. Still wondering how I'm going to get all off these connected to each other.

[Floopy]

I got everything routed. It was all grand and great until I had to get all the interrupts wired up. I hope it won't affect performance too bad. I'm only running it at 1Mhz.
It would cost around 28$ for 10 of them.(JLCPCB)

[cbmeeks]

Speaking of JLCPCB, I'd like to mention that I recently used them for my Potpourri6502 computer. In their documentation (https://support.jlcpcb.com/article/28-h ... on-the-pcb), they claim if you want to move the customer ID to a custom location, you can just create a label with the text "JLCJLCJLCJLC" and they will print the customer ID there.

So I made sure the font size was large enough and put "JLCJLCJLCJLC" on the back of my board. When I got my boards in, they literally printed "JLCJLCJLCJLC" on the back and went ahead and printed the customer ID on the front of the board.

I contacted them about this but have not heard back.

Maybe they don't support that feature on the back of the board. But I didn't see it mentioned in the docs. Maybe they literally require the quotation marks...I don't know. But I'm a little irritated they haven't responded yet.

I can't complain too much since my board is a pretty good size (about the size of an NES cartridge) and I added the extra $9 color charge for red. Total cost including shipping was in the low $40's for 10 boards.

Anyway, FYI.

[Floopy]

cbmeeks wrote:

Speaking of JLCPCB, I'd like to mention that I recently used them for my Potpourri6502 computer. In their documentation (https://support.jlcpcb.com/article/28-h ... on-the-pcb), they claim if you want to move the customer ID to a custom location, you can just create a label with the text "JLCJLCJLCJLC" and they will print the customer ID there.

So I made sure the font size was large enough and put "JLCJLCJLCJLC" on the back of my board. When I got my boards in, they literally printed "JLCJLCJLCJLC" on the back and went ahead and printed the customer ID on the front of the board.

I contacted them about this but have not heard back.

Maybe they don't support that feature on the back of the board. But I didn't see it mentioned in the docs. Maybe they literally require the quotation marks...I don't know. But I'm a little irritated they haven't responded yet.

I can't complain too much since my board is a pretty good size (about the size of an NES cartridge) and I added the extra $9 color charge for red. Total cost including shipping was in the low $40's for 10 boards.

Anyway, FYI.

I'll remove it, I just put it there because I could.

I'll send it to the fab.

[BillO]

On the subject of PCB makers, I find PCBWAY has better shipping options (their ePacket is pretty good and fast for the price - usually $10CDN) and JLCPCB is much better price for 4-layer boards.

[cbmeeks]

Floopy wrote:

I'll send it to the fab.

I'm not saying it won't work for you...just that it didn't work for me. Your mileage may vary, as they say.

To be fair, the customer ID isn't the end of the world.

When I do my first expansion card for the Potpourri6502, I plan on doing a panel design where they can leave it off completely by putting it on the outer cutting area.

[Floopy]

The boards came in and I'm very pleased with the quality. Thankfully they put the customer ID under the crystal oscillator can. I didn't have time to make a proper program, but I wanted to verify that it was reading the EPROM properly. In the picture it's just running a loop that sends it back to $8000 every time it reaches $8003.

What I would do different:
-Install a ZIF socket for the ROM. I wanted to do this originally but I forgot about it later on.
-Use fewer IC's. Next time I'll use only on 74XX device instead of two.

Thank you everybody who contributed!

[BillO]

Congratulations.

Fun and satisfying, isn't it?

[Floopy]

BillO wrote:

Congratulations.

Fun and satisfying, isn't it?

Yes it is, I've been accumulating parts and gear for over a year for this!

[Floopy]

So far so good (except the buttons and the jumper that selects the CPU being wired wrong)

Although I'm struggling to get the 6522 to work. I don't know what I'm doing and it's obvious....

I'm trying to write to port B. I writing to the internal register 0000 and probing the outputs, but everything is high. I don't get a single line that is low.
What am I doing wrong? The program just loads $#01 into the accumulator and then stores it at address $6000.