SCC's SC516 w/SIO SC511 doesn't accept input in CPM

[Joel Burton]

I have a otherwise-working SC516 (that's Z80 w/RAM+ROM on one card) and the SC511 (SIO+CTC0. The SIO and CTC are jumpered to the defaults.

I can run CPM fine w/o the SIO card, using the on-board bit-banging; that uses CPM-E (and, naturally, at 9600 baud) 

I want to use CPM with the SIO, though. With the SIO installed, the SCM monitor works fine and reports the SIO connected, and it runs at 115.2k.

When I've installed CPM-F (which should work for my setup; Z80 SIO at 0x80 + CTC at 0x88 (at 1.8432 MHz)), I get the CPM welcome message and an "A>" prompt, but no response on the keyboard when I type anything.

Any ideas would be appreciated!

- Joel

[Ronny Ribeiro]

Hello, Joel,

I have this exact configuration running here: SC516 + SC511, with configuration F1 20221016 as detected by SCM. 

From SCM, SIO lists at @80, CTC @88 and CF Card @90.

Everything is working fine.

I remember running on an issue like yours, and it was related to conflict of bios version and device address.

Hope this helps.

Regards,

Ronny

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[Steve Cousins]

It could be an issue with the interrupts from the SIO. SCM does not use interrupts for the SIO but the CP/M BIOS does. If interrupts from the SIO are not working the character receive from the terminal will not work.

Steve

[Joel Burton]

Ronny and Steve --

Thanks for the replies!

Ronny says config F1 works for him; my reading of https://smallcomputercentral.com/articles/installing-cp-m-2-2-with-scm/ suggests that CPM-F should use "SCM F2 v1.3 (2022-02-27) or later", so I've flashed my ROM to that. With F2, I *must* use the SIO even to get the SCM (and CPM doesn't work since it's with the SIO). Earlier in my troubleshooting, I had "SCM F1 v1.2.1 (2022-02-16) or later" flashed and the SCM worked under both SIO and bit-banged, but CPM only worked with bit-bang (of course, I was using a CF with CPM-E for bit-bang and CPM-F for trying SIO)

Which should I be trying for SIO+CPM? F1 or F2?

Steve: I just have these three cards (SC511, SC516, SC504), and none have jumpers related to interrupts, nor does the baseboard (SC513). I'm mindful of the text on the PCB pointing out that highest interrupt prioririties go toward the front (where the power plug is), and I've tried a few different orders of the cards (and always starting at the front, without gaps between them). Is there a certain order?

Thanks :) - Joel

[Joel Burton]

RESOLVED!

Steve gave me some off-channel advice and I checked all the interrupt stuff carefully. It appears that once I entered CPM and first tried to type a character, IEI got stuck, which it shouldn't do.

Trying out a lot of things on the SC511 (SIO+Clock), I found that my SIO shorted to 5V somehow. It looks like the chip was damaged (perhaps by me if I mis-inserted something?). Replaced with another SIO/2 and it works fine.

Some things learned:

- it is F1 ROM that I should be using here
- it was interesting to watch my logic analyzer for the NMI/IEI stuff
- a great debugging tip is to walk your multimeter up and down on all the card pins; other than the 2 pins for 5V and the 2 pins for GND (which are obviously shorted in those pairs), the only other short was M1 + 5v. I pulled the SIO chip first and found no short on the card anymore, and the M1+5v were shorted on the chip.

It's interesting that everything other than CPM was working -- I guess the CF reader, the digital IO board, and the CTC itself must not care about the state of M1 (since those all worked). It's also interesting that SIO-outside-of-CPM works; I guess the serial driver for CPM must do something with M1 and failed since it would never go low.

Anyway, thanks to Ronny and to Steve for ideas! Y'all are the best.

J.

[Ronny Ribeiro]

Hi Joel,

I'm very glad to hear that!

I love this SC500 series. I have all the boards Steve created for this platform which allow me to instantly put together very specific setups. 

I found it so beautifully designed that I didn't bother to get it a case.

I use the upper holes to tie the boards together with nylon standoffs, which, along with the boxed connectors, makes everything sturdy as a rock.

This hardware robustness is also seen with a 10MHz z80 overclocked to 14 MHz: every board that I have, SIO, PIO, CTC, ACIA, etc, works flawlessly with the CPU at this speed.

I hope you can now enjoy your little neat computer!

Best regards,

Ronny

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