Computer Old Farts Forum
 help / color / mirror / Atom feed
From: Derek Fawcus <dfawcus+lists-coff@employees.org>
To: Clem Cole <clemc@ccc.com>
Cc: Computer Old Farts Followers <coff@tuhs.org>
Subject: Re: [COFF] DEC terminal line driver chips?
Date: Fri, 30 Apr 2021 17:49:29 +0100	[thread overview]
Message-ID: <YIw1GbWGRhXOyBmw@clarinet.employees.org> (raw)
In-Reply-To: <CAC20D2M4O4La0VZWsnrpTqCaf5MBTn4o5pK+xhffXJ=BJuTpNg@mail.gmail.com>

On Thu, Apr 29, 2021 at 09:17:27AM -0400, Clem Cole wrote:
> If you look at the schematics for the VT-100 (which are available on
> bitsavers) as well as most terminals of the day used the
> Motorola MC1488/1489 driver pairs [early on, TI marked them as 75488/75498
> but I doubt you'll see that old].
> 
> Anyway, for any terminal of those times, I'd be surprised if the later
> devices (like VTx20 series) did not them [the issue with these devices is
> you need all of 5 and +/- 12 volts].   These terminals are new enough that
> they might have used MAX232 (single 5 v power - there are even 3.3v
> versions these days).  All of these devices are very available online.  I
> would suggest putting high quality (*i.e.* auget style / machined pins)
> sockets.  The nice thing about 1488/1489 is that they were doped to fuse
> the output section on failure, so just replacing them will in fact
> resurrect most serial port failures.  Frankly, I never understood why more
> manufacturers did not put them in sockets for easy replacement.

Well even in 1988 when I entered industry for a year (as an EE), the MAX232
was quite new (looks ike it was introduced in '87), and plenty of designs
still used the 1488/1489 chips.  I do recall that those I worked with at the
time were often produced with turned-pin sockets, specifically to allow the
chips to be easily replaced.

It seemed to be around 91-92 before the MAX232 was common in new designs,
certainly I used it for adhoc test equipment around that period.

I guess familarity, and the the time for the design pipeline to flush out
may have had a effect, only using it on new designs, or reworks where the
PCBs had to be redesigned due to chips going out of production.

DF
_______________________________________________
COFF mailing list
COFF@minnie.tuhs.org
https://minnie.tuhs.org/cgi-bin/mailman/listinfo/coff

      parent reply	other threads:[~2021-04-30 16:57 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-29  7:02 Tom Ivar Helbekkmo via COFF
2021-04-29 12:21 ` Brad Spencer
2021-04-30  7:34   ` Dave Horsfall
2021-04-30 11:55   ` Tom Ivar Helbekkmo via COFF
2021-04-29 13:17 ` Clem Cole
2021-04-30  7:42   ` Dave Horsfall
2021-04-30 12:12   ` Tom Ivar Helbekkmo via COFF
2021-04-30 16:49   ` Derek Fawcus [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YIw1GbWGRhXOyBmw@clarinet.employees.org \
    --to=dfawcus+lists-coff@employees.org \
    --cc=clemc@ccc.com \
    --cc=coff@tuhs.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).