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

52 views
Skip to first unread message

Joel Burton

unread,
Dec 15, 2025, 3:12:45 AM (3 days ago) Dec 15
to retro-comp
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

unread,
Dec 15, 2025, 7:34:15 AM (3 days ago) Dec 15
to Joel Burton, retro-comp
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


--
You received this message because you are subscribed to the Google Groups "retro-comp" group.
To unsubscribe from this group and stop receiving emails from it, send an email to retro-comp+...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/retro-comp/20f1b881-2280-44fc-9e70-01c1c307bf76n%40googlegroups.com.

Steve Cousins

unread,
Dec 15, 2025, 1:35:26 PM (3 days ago) Dec 15
to retro-comp
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

unread,
Dec 15, 2025, 2:04:47 PM (3 days ago) Dec 15
to retro-comp
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
Reply all
Reply to author
Forward
0 new messages