clements@BBNCCQ.ARPA (Bob Clements) (10/07/85)
>> Anybody know what hardware was originally responsible for the >> use of 150 baud? ... Who made the first 15 cps printer? The first major printer at 150 baud (maybe the first of all, I don't know) was the Teletype model 37. Its mechanism was a lot like the model 35, but with a bigger type basket. It was Teletype's first machine with lower case letters. We used them on some of the early PDP-10 processors as consoles. [We = DEC engineering of about 1969.] And the person who corrected the tutorial by saying that 150 baud machines used two stop bits was wrong. The model 37 used one stop bit. I think the 37 was the only machine I ever saw that was fully mechanical at that speed. That is, the "UART" function (serial <--> parallel conversion) was mechanical, not electronic. It rattled its little heart out at a good clip, but couldn't really stand up to the effort. They didn't last long before wearing themselves out and dying. /Rcc ARPA: CLEMENTS@BBN.ARPA USENET: {ihnp4, decvax, ...}!bbncca!clements Ham Packet: K1BC Telco: 617-497-3612
bower@dca-eur.ARPA (10/07/85)
Must strongly disagree with the statement that Model 37's wear
out fast. I have one (currently in storage) that was the ONLY printer
on my home system(s) for over 3 years, often printing large assembly
listings lasting over 6 hours. As long as you gave them an annual oil
change and lube, they will last almost indefinately. The one I have
is set for 10 pitch, although I understand some were 12-pitch, and
printed only 69 characters before inducing an automatic line feed.
The 150 bps speed appears to be an early effort into the standard
rates governed by the "75 times 2 to the nth" rule comprised of 75, 150,
300, 600, 1200...etc bit rates.
One quirk on some Model 37s is that many had the MIL-STD-188C inter-
faces which use a POSITIVE voltage for a logical "1" whereas RS-232 uses
a NEGATIVE voltage for a logical "1". This means that an extra inverter
is required when driving the device from commonly available interfaces.
Hal