SC114 cp/m and xmodem

[Nick B.]

Hi,

Not having much luck trying to get CP/M files transferred over the bit bang serial port on SC114, SC729 and 128MB CF card. I've prepared the card using the files from the CPM-A set on smallcomputercentral.com which leaves me with drives A-P formatted and download.com on A:.

Grant's download.com seems to work occasionally but most of the time either fails on checksum or file length errors. I have managed to get a copy of xmodem.com but I cannot get it to start a receive session, if I start it from XMODEM SOMEFILE.COM /R /C /X0 it just hangs. It does transfer files in the opposite direction successfully. I have tried this with both Minicom and Teraterm. I've also tried a couple of different FTDI USB serial interfaces. I think my next step will be to add a console port wusing the ACIA or SIO/2 if I can't get this working.

I did see a thread about this back in August 2023 but the BIOS I have is dated BIOS-A (2023-06-10) so maybe I'm missing an update to this somewhere?

Thanks

Nick

[Mark Cohen]

Maybe make sure cf card is close to CPU card.

Also I'm using XM version of xmodem

Settings have RTS/cts

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[David Lochlin]

I had this issue some time back. I could not get Terraterm to work with the transfers but ExtraPuTTY works as long as you are using CTS/RTS/ Your FTDI needs to support this. See my last post here https://groups.google.com/g/rc2014-z80/c/ngCnL83aSfc

Dave

[David Latham]

Is it a flow control thing? 

[Nick B.]

I've tried several FTDI converters. They appear to have RTS/CTS so next step then is to get my oscilloscope out and see if it actually works.

In the meantime I've managed to get a few essential files on there by reading/writing a copy of the card with dd then using cpmtools.

Thanks for the hints so far.

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[Nick B.]

Some success.

I found the USB-C FTDI converters didn't seem to support RTS/CTS, noticeable when trying to use download.com. Then went back and read the docs for the SC114 at smallcomputercentral.com and realised I was setting ASCII delays in Teraterm. Once I set all these to zero and enabled RTS/CTS, transfers to download.com now work properly with both Teraterm and Minicom.

Xmodem (XMODEM 2.7 By M. Eberhard) still mostly unsuccessful but has worked on the odd occasion after hanging for tens of seconds. Otherwise all I see is RETRY 0 NAK ON SECTOR. Xmodem send works fine as does Zmodem (ZMTX.COM). Zmodem RX does not work, I see the initial data sent out and it accepts ^x^x^x to cancel it.

Next step will probably to add a serial card.

Nick.

[Nick B.]

I should have added I'm now using the original USB mini-B FTDI converters.

[Mark Cohen]

Most of the FTDI chips I have bought are fake now.

They used to be good but now pretty much 90% seem bad.

My test is to see if I can do a firmware upgrade.

If it halts or does not start then it is fake.

This works 100% of the time and I have bought many of them.

https://www.amazon.com/dp/B0D9BDJBKK?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_13

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[Nick B.]

Thanks I've ordered a couple of those to evaluate from amazon UK.

I've not tried updating the firmware. Do FTDI have a tool for this or is it part of the normal Windows update process?

[Jaap van Ganswijk]

Do you people know of the xon/xoff protocol? It's two special characters that have priority over the normal data flow and work like cts etc. Please check online for details, because it's decades ago that i had to deal with these kinds of problems...

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[Alan Cox]

Xon/xoff is extremely problematic with a lot of transfer protocols because it effectively eats two in band symbols and forces you to start using additional quoting/encoding as your line is no longer 7 or 8bit clean.

Xmodem requires a clean line so xmodem + xon/xoff doesn't work. Kermit can work this way and some of the other protocols.

[Richard Deane]

8086.net sells some little usb serial  adapters that do rts/cts, and bill shen has documented how to cut a trace and solder a wire to make other adapters do rts/cts. (https://retrobrewcomputers.org/doku.php?id=builderpages:plasmo:epm240dev:3vz80:3vz80rev1_1)

Richard

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