Yes.
The chips I used were the engineering sweet spot for my task. The 1620 logic levels are
{ground, resistive pulldown to -12V}. The 1488 (plus clamp diodes) makes the right
levels. Shame about the part number but it's not the chip's fault. By injecting
current on the 1489's Response Control pins, I could level shift from 1620 to TTL with
low cost and part count.
Dave Wise
________________________________
From: Mike Stein via cctalk <cctalk(a)classiccmp.org>
Sent: Sunday, February 2, 2025 1:10 PM
To: General Discussion: On-Topic and Off-Topic Posts <cctalk(a)classiccmp.org>
Cc: Peter Corlett <abuse(a)cabal.org.uk>uk>; Mike Stein <mhs.stein(a)gmail.com>
Subject: [cctalk] Re: RS232 then and now
These days you can get rs232<>TTL converter modules for less than the price
of a MAX... chip; 3.3-5V (no 12V), only slightly larger than a MAX chip
only; for an extra buck or so you can get it with a DE-9 connector
On Sun, Feb 2, 2025 at 7:41 AM Peter Corlett via cctalk <
cctalk(a)classiccmp.org> wrote:
On Sat, Feb 01, 2025 at 11:01:34PM +0000, Chuck Guzis
via cctalk wrote:
On 2/1/25 13:12, David Wise via cctalk wrote:
[...]
I used
the 1488 and 1489 RS232 chips as level shifters on the
semiconductor RAM board I designed for the IBM 1620. Handy.
In the 1970s/80s, there seemed to be two camps of though WRT EIA
receivers/drivers. There was the Motorola 1488/1489 crowd than there was
the TI crowd (75150/75154). Never bothered to ask which had advantages
over the other.
They're still sold and the datasheets are readily-available, so the
advantages can be quickly determined: On paper, the 75150 is faster and
slightly less power-thirsty than the 1488, but contains just two drivers
instead of four. It also costs over twice as much. So between the two of
them, the 1488 is the winner, especially if you need more than TxD and RTS.
My experience with ye olde Amiga was that its 1488/1489 serial drivers got
rather toasty and would occasionally go bang. I've not knowingly used the
75150, but that might just mean that it quietly gets on with its job
without
incident and I haven't had to desolder the crunchy remains...
These days, the MAX232 (or better, one of the clones which doesn't need
chunky electrolytics) is the obvious choice, even if you have +/-12V
available on your board: it's cheaper and takes much the same board space
as
than the two-chip 1488/1489 (if five-wire serial is good enough), works off
the +5V that's everywhere on your board so you save having to make space to
route the +/-12V to it, and doesn't burn your finger when you touch it.
Also, the number 1488 is somewhat unfortunate, especially given current
events.