Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!swrinde!ucsd!ucbvax!RICHTER.MIT.EDU!krowitz
From: krowitz@RICHTER.MIT.EDU (David Krowitz)
Newsgroups: comp.sys.apollo
Subject: Re:  Help with getty and/or /etc/ttys at 10.2
Message-ID: <9010031349.AA05275@richter.mit.edu>
Date: 3 Oct 90 13:49:41 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 66

/dev/ttyXX devices are tricky. If you use /com/tctl to look at the line
settings, you'll find that the settings look something like this:

$ tctl -line 1
Status of Line 1: 
Erase (character delete) character: 08 (hex)
Kill (line delete) character: 18 (hex)
End of file character: 1A (hex)
Quit character: 03 (hex)
Fault character: 1D (hex)
Suspend character: 10 (hex)
New line delay: 0 
Speed: 9600
Raw: FALSE,         Echo: TRUE,         Cvt_NL: FALSE
CvtRaw_NL: FALSE,   Host_Sync: TRUE,    Input_Sync: FALSE
RTS: TRUE,          DTR: TRUE,          DCD: TRUE
CTS: TRUE,          Quit_Enable: FALSE, Fault_Enable: FALSE
Susp_Enable: FALSE, DCD_Enable: FALSE,  CTS_enable: FALSE
BP_Enable: FALSE,   RTS_Enable: FALSE
Eight bits per character, Parity: None, One stop bit
Errors enabled: FRAMING 
Polite: FALSE,      Wait for DCD: TRUE,       

Notice that "Wait for DCD: TRUE"? It means that the line will refuse to
respond to incoming characters until it sees the Data Carrier Detect
line set. This is a pin that is not wired in most null modem cables used
for simple dumb terminals. In the example above, DCD is TRUE because I
actually have a modem (well, in truth, an IDSN telephone's data port)
connected to my RS232 port will a full modem cable. Most terminal cables
are either wired for XON/XOFF handshaking with the following:

pin1  -- pin1      frame ground
pin2  -- pin3      transmit/receive
pin3  -- pin2      receive/transmit
pin7  -- pin7      signal ground

or they are wired for CTS/RTS handshaking with the following:

pin1  -- pin1      frame ground
pin2  -- pin3      transmit/receive  (I may have the tran/rcv reversed?)
pin3  -- pin2      receive/transmit
pin6  -- pin20     clear-to-send/data-terminal-ready
pin7  -- pin7      signal ground
pin20 -- pin6      data-terminal-ready/clear-to-send

Pin 4 may also be jumpered locally to pin 6 on both ends so that both
clear-to-send (CTS) and request-to-send (RTS) will be active.

I think DCD is pin 8. I could well be wrong. Different manufacturer's
manual's sometimes yield a different set of names. At any rate, you
need to jumper the DCD pin to something which is TRUE (DTR is a good
one) in order to use /dev/ttyXX.

On the other hand, you can use /dev/sioX instead of /dev/tty0X. Even
though they both refer to the same S
RS232 line, the /dev/sioX device
ignores the DCD line state while the /dev/tty0X device handshakes
on it.


 -- David Krowitz

krowitz@richter.mit.edu   (18.83.0.109)
krowitz%richter.mit.edu@eddie.mit.edu
krowitz%richter.mit.edu@mitvma.bitnet
(in order of decreasing preference)