Subject: Problem w/ serial console after power-on

From: Jan-Benedict Glaw <[email-masked]>
Date: Wed, 11 Oct 2000 01:38:04 +0200

Hi!

I've got a DECStation 5000/120 and tried to start some hacking,
but no success: I can read everything the box outputs to its
serial lines, but anything I type into my minicom seems to end
up in /dev/null... The cable is okay, but what could be wrong
instead? Any hints?

=================================================================
KN02-BA V5.7e
3/misc/kbd
?STF (4: Ln#0 Kbd self test)

3/misc/mouse
?STF (4: Ln#1 Pntr self test)

?IO:  3/rz0/vmunix  (bb rd)
=================================================================

MfG, JBG

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---

From: Karsten Merker <[email-masked]>
Date: Wed, 11 Oct 2000 07:48:50 +0200

> up in /dev/null... The cable is okay, but what could be wrong

Well known effect :-)
I have a "normal" 7-wire-nullmodem cable that works fine when connecting
my vt420 to my Linux PC and running a getty on the port, ist also works
fine when connecting the vt420 to the DECstations serial console port, but
I have the same problem as you when connecting the DECstation to the PC
and running a terminal emulation program on the PC.

The soloution: use a 3-wire-nullmodem cable and inside each of the
connectors connect RTS-CTS and DTR-DSR-DCD.

This should look like this:

DECstation           PC

GND ---------------- GND

RxD ---------------- TxD

TxD ---------------- RxD

RTS -+            +- RTS
     |            |
CTS -+            +- CTS

DTR-+             +- DTR
    |             |
DSR-+             +- DSR
    |             |
DCD-+             +- DCD

Viel Spass beim Loeten :-).

Greetings,
Karsten
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---

From: Jan-Benedict Glaw <[email-masked]>
Date: Wed, 11 Oct 2000 09:18:32 +0200

> On Wed, Oct 11, 2000 at 01:38:04AM +0200, Jan-Benedict Glaw wrote:

[Nonfunctional null modem cable]

> I have a "normal" 7-wire-nullmodem cable that works fine when connecting

Yes, that's true...

> connectors connect RTS-CTS and DTR-DSR-DCD.

Oh, where's my foot? ...want to shoot it;)

> Viel Spass beim Loeten :-).

...und ich wollte den gestern schon von meiner Freundin mitnehmen...

MfG, JBG

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From: Ralf Baechle <[email-masked]>
Date: Wed, 11 Oct 2000 17:35:36 +0200

> Oh, where's my foot? ...want to shoot it;)

No probleem with knocking out hardware handshaking of the serial console
like that.  You can't do rts-cts or you risk hard to track temporary
freezes of the machine.  It's been what has caused the freezes of
oss.sgi.com some time ago ...

  Ralf