FTDI USB-C working, but not with XMODEM transfers...

[MogensB]

Hi,

I recently bought a couple of cheap chinese FTDI adapters with an USB-C connection, to replace two mini-USB adapters.

They work nicely when I run interactive terminal sessions using TeraTerm, no problems, but when i want to do an xmodem transfer from TeraTerm to the target CP/M system (I have tested with both the SC131 and the SC114), it fails (no progress). I can do XMODEM from CP/M to TeraTerm.

My first thoughts are something HW handshake related, but I've tested that the FTDI232RL chip pins are indeed connected to the correct pins. Also tried downloading latest FTDI VCP drivers for my Windows 11, but no luck.

I have tested 2 adapters, both have the same issue. Also tested both Windows and Linux host systems, if drivers were an issue, but observe the same problem. When I switch back to the older FTDI everything works as expected.

The newer ones not working has an FTDI chip marked C8728390 / FT232RL and the older working ones are marked RTC2326A.

Does anyone have experience with FTDI USB-C adapters and TeraTerm XMODEM transfers? And any hints on troubleshooting will be appreciated.

Or maybe someone here has a reference to an FTDI USB-C adapter known to work as replacement for the mini-USB ones, including XMODEM transfers.

Best regards,

Mogens from Denmark

[Wayne Warthen]

There is a test to determine if flow control is working in this thread:

https://groups.google.com/g/rc2014-z80/c/Dkzr_3kTDRE/m/v2XMcUGaBgAJ

Suggest you try this next.  I am out of town through the weekend, but will try to help further when I return.  Would like to know results of test above first.

Thanks, Wayne

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[Wayne Warthen]

Also, on Z180 serial ports you can use RomWBW MODE command to lower baud rate.  Try 9600 baud.  At that baud rate XModem should work even if flow control is broken.

Thanks, Wayne

[Ronny Ribeiro]

Hello Mogens,

I have the same FTDI USB-C adapter, and it's working perfectly on my Z180 (SC503) under CP/M 2.2 with RomWBW. 

I'm using Minicom on Ubuntu and I have both hardware and software flow control active on the terminal connection.

Regards,

Ronny

[MogensB]

Hi,

Observation #1: Using TeraTerm to paste 20 lines of ABCDEFGHIJKLMNOPQRSTUVWXYZ into the terminal indicates loss of characters at 115200 baud (see screenshot)

Observation #2: On my SC131 I have now tested different baud rates from 9600 up to 57600, using the MODE command in CP/M, and it is transferring files via XMODEM flawlessly. Next step 115200 baud, and then it fails.

As I interpret these observations, the hardware handshake is not performing as expected in the FTDI adapter.

/Mogens

[Wayne Warthen]

Your observations definitely suggest an issue with hardware flow control (RTS/CTS).  Since you have already confirmed that the RTS/CTS pins are properly connected by the adapter board, I suspect that you have fake FTDI chips on the Chinese adapters.  This is, unfortunately, quite common.  And the flow control issue is specifically one of the problems encountered with them.

If you want to do further testing, I think you need to put an oscilloscope on the RTS signal and capture what is happening when doing the RTS/CTS test process.  Even that may not be conclusive based on previous posts.  It has been suggested that on the fake chips, the RTS/CTS signals have insufficient drive.  So, they may appear to be working even when they are not.

Thanks, Wayne

[Mogens Bramm]

Thx Wayne, for your feedback!

Both adapters will soon end their days as electronics for recycling. And I will be looking for another product, hopefully better quality.

Best regards,

Mogens

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