RS232 Voltage Levels

[Jim Thompson]

On Fri, 06 Jan 2006 09:46:11 GMT, Robert Baer

[snip]

There may still be some devices that will convert RS-232 levels to
TTL and some that go the other way.

RS-232 -> TTL = MC1489

TTL -> RS-232 = MC1488

These chips are still available more than 40 years after I designed
them ;-)

These chips adhere to the original RS-232 spec.
<snip>

1488 requiring several supplies -- and runs hot as a pistol, too.

360mW typical ;-)

I've
got a box of both; they were about all there was to use in the market
and worked well when I was using them; but don't use them much now
because of the power requirements (especially the 1488) and the
serious heat to be removed (again the 1488 much more than the 1489, if
memory serves, but neither of them slouches in the heating
department.)

Jon

Keep in mind this was early '60's.

Quite a few process capability improvements since then.

...Jim Thompson

 

[Roy L. Fuchs]

On Fri, 06 Jan 2006 09:46:11 GMT, Robert Baer

[snip]

There may still be some devices that will convert RS-232 levels to
TTL and some that go the other way.

RS-232 -> TTL = MC1489

TTL -> RS-232 = MC1488

These chips are still available more than 40 years after I designed
them ;-)

These chips adhere to the original RS-232 spec.
<snip>

1488 requiring several supplies -- and runs hot as a pistol, too. I've
got a box of both; they were about all there was to use in the market
and worked well when I was using them; but don't use them much now
because of the power requirements (especially the 1488) and the
serious heat to be removed (again the 1488 much more than the 1489, if
memory serves, but neither of them slouches in the heating
department.)

Sounds like a poorly implemented utilization. Sum Ting Wong must
have done the design.

 

[Roy L. Fuchs]

On Fri, 06 Jan 2006 09:46:11 GMT, Robert Baer

[snip]

There may still be some devices that will convert RS-232 levels to
TTL and some that go the other way.

RS-232 -> TTL = MC1489

TTL -> RS-232 = MC1488

These chips are still available more than 40 years after I designed
them ;-)

These chips adhere to the original RS-232 spec.
<snip>

1488 requiring several supplies -- and runs hot as a pistol, too. I've
got a box of both; they were about all there was to use in the market
and worked well when I was using them; but don't use them much now
because of the power requirements (especially the 1488) and the
serious heat to be removed (again the 1488 much more than the 1489, if
memory serves, but neither of them slouches in the heating
department.)

Sounds like a poorly implemented utilization. Sum Ting Wong must
have done the design.

PS: I refer to the circuit designer, not the chip.

 

[Jonathan Kirwan]

On Fri, 06 Jan 2006 09:46:11 GMT, Robert Baer

[snip]

There may still be some devices that will convert RS-232 levels to
TTL and some that go the other way.

RS-232 -> TTL = MC1489

TTL -> RS-232 = MC1488

These chips are still available more than 40 years after I designed
them ;-)

These chips adhere to the original RS-232 spec.
<snip>

1488 requiring several supplies -- and runs hot as a pistol, too.

360mW typical ;-)

Connected and driving, it sure seemed like more! But I think the
RthetaJA was about 150. Which meant 'damned hot' even at .36W.

With as little as 4k or so on the 1489 receiver inputs, that was
getting near another tenth watt dissipation per connected input at
that end, with +/-12-15V signaling applied, too. Part of the spec,
sure; but still ...

There was an advantage to all this, I suppose. I could find the 1488
and 1489 parts blindfolded. Just casually feel where the heat is
emanating from.

Keep in mind this was early '60's.

Quite a few process capability improvements since then.

No doubt. I didn't get around to using them until much later, though,
being that I was in grade school in the early '60s.

Jon

 

[Charles Jean]

No delay should be required.

-- Dave Tweed

___

I'm the OP of this thread and would like to thank everyone for such a
voluminous and knowledeable response! For those that wanted to know,
the chip is the SV2000 video interface chip from
http://www.speechchips.com. It inputs serial ASCII data and converts
to an RS170 composite video encoded stream. It is supposed to give a
9 line X 16 character display, with a standard ASCII font as well as
user-defined fonts. Control commands are preceeded by ASCII 27(ESC).
It has been marked down from $20 from $10. I already had a portable
BW TV with a composite video input, so I thought I might try it. By
bit-banging I wouldn't use the precious single UART of my uC, and only
one of its output pins.

As you can see from the data sheet, the connection on pin 6 allows for
either "normal" or "inverted" TTL levels to be used. I think I could
have saved lots of confusion by rephrasing my question to: "What's the
idling voltage of normal and inverted TTL serial lines?" I can write
the program to have the line at pin 3 idle at either 0 or 5 volts, and
I had a 50-50 chance of having pin 6 wired correctly. Just lazy
again. Sorry if I caused any trouble.

 

[Michael A. Terrell]

"Jim Thompson" wrote ...

...
Charles Jean wrote:

Who's Mark?

[snip]

Space's brother ?

ROTFL! )

(But likely lost on the younger crowd.)

Yeah, they don't know what they missed by never working on the old AP
& UPI newswire KSR33 teletypes on a leased loop.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Don Bowey]

"Jim Thompson" wrote ...

:
...
Charles Jean wrote:

Who's Mark?

[snip]

Space's brother ?

ROTFL! )

(But likely lost on the younger crowd.)

Yeah, they don't know what they missed by never working on the old AP
& UPI newswire KSR33 teletypes on a leased loop.

Or the models 14, 15 and 19 that were even before your time. They seemed
hi-tech at the time. My first one at home was a 14 with the range crank on
top, front. It came from a Telco Toll office.

 

[Roy L. Fuchs]

"Jim Thompson" wrote ...
:
...
Charles Jean wrote:

Who's Mark?

[snip]

Space's brother ?

ROTFL! )

(But likely lost on the younger crowd.)

Yeah, they don't know what they missed by never working on the old AP
& UPI newswire KSR33 teletypes on a leased loop.

Or the models 14, 15 and 19 that were even before your time. They seemed
hi-tech at the time. My first one at home was a 14 with the range crank on
top, front. It came from a Telco Toll office.

Well... take a bow.

 

[Mark Zenier]

Yeah, they don't know what they missed by never working on the old AP
& UPI newswire KSR33 teletypes on a leased loop.

33's were uppercase ASCII. I think the wire services used 5 bit machines.
The ones with the type box were 28s. I think the 5 bit code corncob
machine was the 32.

Mark Zenier [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)

 

[Michael A. Terrell]

Or the models 14, 15 and 19 that were even before your time. They seemed
hi-tech at the time. My first one at home was a 14 with the range crank on
top, front. It came from a Telco Toll office.

I had a model 15 of my own, (Found at a Dayton hamfest) but I used
the KSR33 a lot more. We had two of them at the military radio & TV
station I worked at in '73 & '74. They replaced our very worn out
Kleinschmidts. Later on I had a Metrodata computer with two 20 mA
boards for AP & UPI news wires at a United Video Cablevision CATV
headend in Cincinatti, Ohio. I was troubleshooting one of the six
channel Metrodata graphics computers when I found a couple undocumented
commands. One that let me interrupt the 20 mA loop. The other let me
type and send messages on a "Read only" system. It wasn't long after
that that the hardwire 20 mA loops were replaced with receive only sat
equipment.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Chuck Harris]

33's were uppercase ASCII. I think the wire services used 5 bit machines.
The ones with the type box were 28s. I think the 5 bit code corncob
machine was the 32.

The wire services used 5 bit machines, such as the model 15, 19, and 28.
The model 15 is what all of us old fogies remember as the intro to US nightly
TV news. They always started and ended with a few seconds of model 15
teletype chatter... Walter Cronkite would fill in the time in between.

The model 32 was a baudot (5 bit) version of the model 33 ascii machine.
It was designed for extremely light duty use, such as a small business
would need for Telex duty. For those that don't know, or remember, Telex
was to business in the 1970's what the fax machine was to business in the
80-90's

 

[Richard Crowley]

The wire services used 5 bit machines, such as the model 15, 19, and
28.
The model 15 is what all of us old fogies remember as the intro to US
nightly
TV news. They always started and ended with a few seconds of model 15
teletype chatter... Walter Cronkite would fill in the time in between.

We would have been better off with 28:30 of TTY SFX.

I just heard a radio spot the other day with TTY SFX in the
background and the announcer using his best "radio announcer"
voice (a parody on news-flash style). It was interesting that the
sound of the old TTYs is so anacronistic these days.

I was a college freshman running the college radio station
solo when they made the mistake and sent the REAL missle
attack message over the wire (instead of the regular sunday-
morning test tape). That gave us a morning of excitement.

 

[Michael A. Terrell]

...

We would have been better off with 28:30 of TTY SFX.

I just heard a radio spot the other day with TTY SFX in the
background and the announcer using his best "radio announcer"
voice (a parody on news-flash style). It was interesting that the
sound of the old TTYs is so anacronistic these days.

I was a college freshman running the college radio station
solo when they made the mistake and sent the REAL missle
attack message over the wire (instead of the regular sunday-
morning test tape). That gave us a morning of excitement.

There are two stories I remember coming across the news wire while I
was at work in broadcast stations. the first was about a tower collapse
at a station that killed most of the tower crew, and just missed the
engineer who dived under one of the old RCA broadcast consoles as the
tower came through the roof and landed on the console. The other was
the murders of "String Bean" (and his wife Ramona) who was a comic on
WSM's "Grand Ole Opry". they were robbed and murdered in their front
yard because he was known to carry a lot of cash on him, due to his
mistrust of banks.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Rich Grise]

"Jim Thompson" wrote ...
:
...
Charles Jean wrote:

Who's Mark?

[snip]

Space's brother ?

ROTFL! )

(But likely lost on the younger crowd.)

Yeah, they don't know what they missed by never working on the old AP
& UPI newswire KSR33 teletypes on a leased loop.

Or the models 14, 15 and 19 that were even before your time. They seemed
hi-tech at the time. My first one at home was a 14 with the range crank on
top, front. It came from a Telco Toll office.

Some guy once gave me what I'm almost sure was a "model 13". It used a 60
mA current loop, and ran at "60 WPM" - that's words per minute, where a
"word" is five characters. So, five characters per second, and five bits
per character, with start and stop bits, that's not very many baud. Back
when I was a young stud with an 8008 and .256 KB of RAM, it wasn't that
hard to make it type stuff. ;-)

Mechanically, it was fascinating. And if you ever get one, don't spray it
with WD-40. On a mechanism like a teletype, WD-40 turns to glue. I spent
about two weeks with a typewriter brush and isopropyl alcohol cleaning
the damn thing up.

But it was kewl, toggling stuff into the ol' Scelbi 8H and having the ol'
model 13 kachunk it out.

Cheers!
Rich

 

[Rich Grise]

.

I'm the OP of this thread and would like to thank everyone for such a
voluminous and knowledeable response! For those that wanted to know,
the chip is the SV2000 video interface chip from
http://www.speechchips.com. It inputs serial ASCII data and converts
to an RS170 composite video encoded stream. It is supposed to give a
9 line X 16 character display, with a standard ASCII font as well as
user-defined fonts. Control commands are preceeded by ASCII 27(ESC).
It has been marked down from $20 from $10. I already had a portable
BW TV with a composite video input, so I thought I might try it. By
bit-banging I wouldn't use the precious single UART of my uC, and only
one of its output pins.

As you can see from the data sheet, the connection on pin 6 allows for
either "normal" or "inverted" TTL levels to be used. I think I could
have saved lots of confusion by rephrasing my question to: "What's the
idling voltage of normal and inverted TTL serial lines?" I can write
the program to have the line at pin 3 idle at either 0 or 5 volts, and
I had a 50-50 chance of having pin 6 wired correctly. Just lazy
again. Sorry if I caused any trouble.

Oh, no trouble at all! We like getting into these lively discussions
and thread-drift. ;-P

Anyway, all I was going to say is try it both ways, especially since
you can do it in the micro. Send it some A's and 5's with '0' idle,
and see what shows up, and send it some A's and 5's with '1' idle,
and see what shows up. At least that's how I'd do it. "RS-232" has
always done that to me.

Good Luck!
Rich