Recycling LOGIN bug [was: Connecting VT100 to 386/ix (thru tty00)]

Jerry H. Chan chan at chansw.UUCP
Mon Mar 19 13:16:29 AEST 1990


In article <8891 at boring.cwi.nl>, leendert at piring.cwi.nl (Leendert van Doorn) writes:
> This worked partially, a getty was spawned and read the input for a login
> name. When I typed my name followed by a cariage return, it executed login
> which immediatly exited. Login was executed (I know, because he asked me

I ran into the same problem using a COM: port on my system; the fix was to
make sure that CD was tied high on the host side, assuming that your COM:
port hardware really looks at that signal (I have seen hardware which
doesn't have traces on the com board to the DB25 connectors for CD). This
was the case for the version of getty / uugetty shipped with ISC 2.0.2; I
don't know if this is a *bug* or a feature :-).

[I will generalize the pinout's for connecting terminals to hosts so that
other readers might benefit.]

If I recall properly (assuming DB25 connectors on each side), here are
the starting pinouts for a typical cable between the host and the terminal:

	Host			Terminal		Notes
	---------------		---------------		-----------------
	1 (Chassis Gnd) <->	1 (Chassis Gnd)		Will work without
	2 (Xmt Data)	->	3 (Rcv Data)
	3 (Rcv Data)	<-	2 (Xmt Data)
	7 (Sig.Gnd)	<->	7 (Sig.Gnd)

The last three lines might look one of two ways, depending on whether your
terminal uses DTR or RTS/CTS flow control, the difference being in the
signal used for flow control -- PAY SPECIAL ATTENTION TO THE CD (8) SIGNAL
ON THE HOST SIDE:

[Note: ISC does not currently support HW flow control for the COM: ports;
 I believe that the FASY drivers do ???]

XON/XOFF FLOW CONTROL:

     Terminal / Host handshake using ^S / ^Q; you can get away with putting
a jumper between pins 20 (DTR) & 8 (CD) on the host side assuming that your
DTR line is asserted high when the port is open (as should be the case):

	Host			Terminal		Notes
	---------------		---------------		-----------------
	8 (CD)		<--\				Loopback
	20 (DTR)	<--/				Loopback

DTR FLOW CONTROL:

     Terminal raises DTR when ready for more data from the host, inverts
when the terminal wants to host to stop.  There is a signal on the terminal
which is forced HIGH as long as the terminal is powered on -- I've assumed
that it is pin 4 (RTS) on the terminal here --

	Host			Terminal		Notes
	---------------		---------------		-----------------
	8 (CD)		<-	4 (RTS)			If RTS is HIGH
	4 (RTS)		->	5 (CTS)
	5 (CTS)		<-	20 (DTR)		Flow control here

RTS/CTS FLOW CONTROL:

     Identical to DTR flow control, except that the RTS (4) and DTR (20)
lines are swapped on the terminal side --

	Host			Terminal		Notes
	---------------		---------------		-----------------
	8 (CD)		<-	20 (DTR)		If DTR is HIGH
	4 (RTS)		->	5 (CTS)
	5 (CTS)		<-	4 (RTS)			Flow control here

Refer to your manual for info regarding the type of flow control used by
your terminal.  Also recommended is a good, cheap break-out box so that
you can see which signals are actually used by your host / terminals.

Hope this helps.

-- 
Jerry Chan 508-853-0747, Fax 508-853-2262  |"My views necessarily reflect the
Chan Smart!Ware Computer Services & Prods  | views of the Company because
Worcester, MA 01606                        | I *am* the Company." :-)
{bu.edu,husc6}!m2c!chansw!chan             \---------------------------------



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