Question about modems

Nigel Johnson nw.johnson at
Wed Nov 13 05:31:05 CST 2019

I actually have an original Hayes 300 modem. Would it be any use if I 
could set it up for a a test, or would it need another genuine Hayes one 
to talk to for what you need?



On 13/11/2019 02:25, Jim Brain via cctalk wrote:
> I am the author of tcpser, a UNIX/Windows program that emulates a 
> Hayes modem.
> Some time ago, Chris Osborn (FozzTexx) forked a copy of my project to 
> fix some bugs and he also added in some parity code, which looks to 
> strip parity from the incoming serial connection (in the case that the 
> serial port is set as 8N1 and the computer attached to it sends in 7E1 
> or similar.
> I am working to merge in all of his changes into the mainline 
> codebase, but I am unclear on prpper Hayes behavior.  His Readme says:
> "I also made the modem routines automatically detect parity and ignore
> it in AT commands and print out modem responses in matching
> parity. Parity is *not* stripped when sending data over the
> connection, which is how a real modem behaves. This may or may not be
> what you want. Some servers will expect an 8 bit connection and may
> not work."
> Did Hayes modem really do that?  I thought most later modems self 
> detected parity and speed and thus would have switched both the comm 
> on the serial port and the data sent to the other side in the same 
> parity (if the terminal was 7E1, the modem would configure as 7E1 and 
> send 7 bit data to the other side.
> But, maybe real modems did as Chris notes. Anyone have guidance on 
> this?  The goal of tcpser is to emulate a Hayes modem as much as 
> possible, but I never really thought about mismatched parity on the 
> RS232 line and how to deal with it.
> Jim

Nigel Johnson

Amateur Radio, the origin of the open-source concept!

You can reach me by voice on Skype:  TILBURY2591

If time travel ever will be possible, it already is. Ask me again yesterday

This e-mail is not and cannot, by its nature, be confidential. En route from me to you, it will pass across the public Internet, easily readable by any number of system administrators along the way.
    Nigel Johnson <nw.johnson at>

Please consider the environment when deciding if you really need to print this message

More information about the cctech mailing list