Grex Hardware Conference

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Grex Hardware Item 11: Sun 2 serial ports, cables
Entered by choke on Thu Sep 5 16:42:21 UTC 1991:

What do the cables look like that connect a Sun 2 to a modem?
I have no such documentation.
Is there a way to configure the scsi tty ports as dce instead of dte?

10 responses total.

#1 of 10 by bad on Thu Sep 5 17:09:24 1991:

Ohh, yeah, we had to create the cables...
STeve or Marcus? Marc, if he remembers?

#2 of 10 by mdw on Fri Sep 6 01:46:45 1991:

The sun-2 serial ports (CPU board and scsi card) are all wired as DTE's.
A straight-through cable should suffice for a modem, in many cases.
Chances are good that the sun will ignore DCD (pin 8) and obey only DSR
(pin 6), so with some types of modems (for instance, Vadic), carrier
detect may not work correctly.  If the modem can't be configured such
that pin 6 is asserted only when carrier is established, you may want to
cross pin 8 from the modem to pin 6 on the computer.  The signals that
the computer apparently uses are:
        1       fg
        2       txd     from computer
        3       rxd     to computer
        4       rts     from computer
        5       cts     to computer
        6       dsr     to computer
        7       gnd
        20      dtr     from computer
Interesting note: this is different from the systech ports on
grex--those are wired up as DCE's.

#3 of 10 by mcnally on Fri Sep 6 04:57:06 1991:

  I suspect he wants information on the SCSI board serial ports.

  Judging from the cable that came with mine, and seems to work fine,
there's no hocus-pocus.  My cable consists of a 50-pin ribbon cable 
with two quick-connect 25-pin D connectors (standard serial connector) 
at one end and a quick-connect 50-pin connector on the other end (two
parallel rows of 25 pins, thin and rectangular..  I could pick it out
of a lineup but don't know what to call it exactly.  It looks like 
things are just wired straight through.  Since there are no wire
crossovers, the only thing that could be reversed is which way the pins
cound on the DB-25s.

#4 of 10 by mdw on Fri Sep 6 06:54:29 1991:

CPU board & scsi board serial ports are almost identical.  Even use the
same chip and software driver, not to mention the same cabling
arrangement and pinout.  The chip used is the Zilog Z8530 duart.  Pin
assignments on any of the 50 pin connectors (CPU J1, SCSI J1 & J2) are:
port A/C/E      port B/D/F
3 txd           28 txd
4 db            29 db
5 rxd           30 rxd
7 rts           32 rts
8 dd            33 dd
9 cts           34 cts
11 dsr          36 dsr
13 gnd          38 gnd
14 dtr          39 dtr
15 dcd          40 dcd
22 da           47 da
24 bsy          49 bsy
It might be worth tracing the lines out--it's not clear to me what, in
fact, is being done with dsr/dcd, or what da,db, and dd are.  Or "bsy"
for that matter.

The Zilog doc I have says the chip supports, per port:
 inputs:        cts,dcd,rxd,rtxc,cts
 outputs:       dtr,rts,w/req,txd
input or outputs: sync,trxc

The zs driver for SunOs seems prepared to read the following signals
from the chip: dcd,cts,rts,dtr, and write: rts,dtr.  dcd is also
apparently what is used for carrier detect - if they don't pull any
weirdnesses going to the port, dsr is ignored on the connector, and dcd,
pin 8, is what one wants connected.  This contradicts the paper
documentation Sun supplies on constructing a null modem cable, which
says to swap 6 & 20, and to ignore 8.  Oh well.  Then again, the Sun doc
also states that carrier detect isn't likely to make sense except with
modems, so perhaps they realize, in some dim manner, that their
directions for a null modem cable doesn't connect anything useful to
dcd.  So it may be best to ignore my earlier thought about crossing 8 to
6.  It doesn't look like the driver does anything with rts/cts.  So
using them for flow control is probably doomed.

#5 of 10 by choke on Fri Sep 6 20:08:09 1991:

 bsy = busy ?
I have the breakouts from the 50-pin connectors to two db25.
What can the second 50 pin connector on the cpu board be used for
besides the SUN 1 mouse and keyboard setup?

#6 of 10 by mdw on Sat Sep 7 09:08:33 1991:

A general purpose 16-bit input-only port.  You could hook up a
simple switch to it, or something.  Perhaps a burglar alarm?

#7 of 10 by choke on Tue Sep 10 00:27:33 1991:

he-haw!
And a 5 volt power supply

#8 of 10 by choke on Tue Sep 10 17:13:11 1991:

aa^H^H^H^HI have no echo?
Yick

#9 of 10 by choke on Tue Sep 10 17:13:46 1991:

It happened again.  How damned odd.  Whenever I go into this editor
drat

#10 of 10 by choke on Tue Sep 10 17:18:20 1991:

There, you can always trust vi.

Well, the straight cable seems to work fine.
The only problem is that my login process doesn't seem to be killing things 
when it loses carrier.  This means that if I hang up on it someone else can
call in and get on as me.
It's kind of sticky dialing out from the tty that has a getty process on it.
My system V machine had a very handy thing called 'ungetty' that would 
make the getty sleep for a while until it got killed.
Anyways, point is it works acceptably.

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