From: kline@cs.arizona.edu (Nick Kline)
Newsgroups: comp.dcom.modems,comp.sys.next.sysadmin,comp.sys.next.hardware
Subject: Re: strange Zyxel modem problem
Date: 22 Jan 93 00:17:11 GMT
Followup-To: comp.dcom.modems
Organization: U of Arizona CS Dept, Tucson

>> my problem: I seem to overflow my modem or have some strange flow
>> control problem
>

>>The default flow control on many UNIX systems is XON/XOFF.  Check the serial
>>port setup and see if "crtscts" (RTS/CTS) is enabled.  Alternatively, if
>>you're logged in via the port, try "stty -a", look at the end of the second
>>line, and see if it says "crtscts" or "-crtscts".
>
>And while we are listing all the things that could conceivably be the
>problem -- is there any chance the modem cable fails to provide
>RTS/CTS?  That is, does it only have two data lines and a ground line?
>If so, and if the modem were set to hardware flow control rather than 
>XON/XOFF flow control, that could be your problem.
>
>I vaguely recall the ZyXEL defaults to RTS/CTS flow control rather
>than XON/XOFF.  So you would ideally want to be sure you have a cable
>that carries those signals, and you would want to configure the 
>serial port on the computer to use RTS/CTS flow control.
>

zyxel uses rts/cts as the default flow control.  the command to do this is
&h3.  I have done that.  In the modem book, it says for the command
&R0 or &R1: rts options
	&r1 : modem assumes rts always on, ignores the changes
	&r0 : delay before cts responds to rts's change
	
&r1 is the default. but after this, it says "This setting is ignored in
async mode. rts is always used as a hardware flow control in this case".

So it seems not to matter.  I tried it anyway and it made no difference.
I also tried the other &h settings, for xon/xoff and no flow control and 
rts/cts  all made no difference

Thanks for all the suggestions.  I do have a correct modem cable. For you
next people, I bought it at NextConnection as a 68040 modem cable. I verified
today that the rts/cts lines are connected as they should be. I did this
by looking at the file about.modem.z, which describes the match ups.

So it is not the cable.  Then I tried cufb, thinking that perhaps I had
a bad cufa port.  This did not fix the problem.

I know I am using rts/cts on the computer side since I am using cufa, a
port which explicitly uses rts/cts, right?

Let me give a more detailed example of how it crashes:

	I can make it overrun things by catting a large file on the machine
i am connected to.  After a while the modem starts to "retrain" (the hs light
flashes) and it either gives up or makes it (50/50 chance).  Often at
this point I "+++" the modem and type ati2, the command which prints out
the state of the modem.  Sometimes, the info, which is perhaps 15 lines
long, is screwed up, in that some parts of it don't come through.  Other
times, the modem goes crazy, and the read_data light becomes constant
as it sends tons of garbage to my screen.  Note that this is all in
command mode.  Nothing should get to the screen when I am typing at
commands.  

For the next person with a zyxel, when your rts/cts stuff is working, does
the cts light ever blink or dim(because it was off for a sec?)?  I ask
this because mine is steady as a rock.

I am going to try to find someone with a 9600 buad modem and swap and
see if we still have problems.

-nick
kline@cs.arizona.edu


Newsgroups: comp.dcom.modems