[GreenKeys] Current Loop to RS-232 Conversion on ASR33
Chris Elmquist
chrise at pobox.com
Tue Mar 19 10:36:20 EDT 2013
It's also true that when '33s were hooked to many microcomputers, they
used a full duplex connection-- two loops, one for keyboard and one
for printer.
I have specific examples of Altair680b, SWTPC 6800, KIM-1, Motorola
MEK6800-D1 and -D2, all circa 1975, 1976 micros where they had a separate
keyboard and printer circuit to the 33 running in 20mA mode, most using
only 12V on the loops.
Chris N0JCF
On Tuesday (03/19/2013 at 09:58AM -0400), Christian Gauger-Cosgrove wrote:
> Ah, well my usual experience is DEC minicomputers, they preferred full
> duplex connections. Mostly because full duplex also didn't echo control
> codes back to the teletype if it didn't need them, and the whole password
> security thing that happened to become prevalent later on.
>
>
> You mention the HP2000; I have no idea about how Hewlett-Packard did
> things, but I am well versed in DEC.
>
>
> Cheers,
> Christian
>
>
>
>
> On 18 March 2013 23:08, <COURYHOUSE at aol.com> wrote:
>
> > **
> > Christian - no the term type for tty would overprint on the hp
> > 2000 as I remember
> >
> > In a message dated 3/18/2013 8:05:47 P.M. US Mountain Standard Time,
> > captainkirk359 at gmail.com writes:
> >
> > Wouldn't computer systems have trended to run an attached '33 as a full
> > duplex terminal?
> >
> > Mostly the reason I can see that is for user logon password protection.
> > (Don't echo back the password.)
> >
> > If the terminal is run half-duplex the terminal needs work arounds -- see
> > for example the IBM 2741's commands to disable printing.
> >
> >
> > Cheers,
> > Christian
> >
> > On 18 March 2013 22:45, Don Robert House <k9tty at dls.net> wrote:
> >
> >> Rob,
> >>
> >> ASCII 67 is an 11 unit code. 1 Start, 8 data bits, 2 Stop. However the
> >> 8th data bit is used for parity.
> >> Since your machine is printing in local you must have a nicely operating
> >> machine.
> >> I have never seen a 33 operate in Full Duplex, but it should certainly be
> >> possible.
> >> The 32, 33, and 38 generate characters in parallel and are serialized by
> >> the distributor.
> >> Your problem is located somewhere incoming to the selector magnet when
> >> the switch is in the Line position.
> >> Your message reads that the machine is not running open so the selector
> >> has constant current in it's winding.
> >> I have some schematic drawings for the 33, but I need to know what model
> >> you have.
> >> There should be a sticker on the rear of the base near the call control
> >> unit.
> >>
> >> Don
> >> K9TTY
> >>
> >>
> >>
> >>
> >> On 16 Mar 2013, at 3:19 PM, Rob Jarratt wrote:
> >>
> >> It has been a little while since I looked at my ASR33 problem. Just to
> >> refresh everyone: In Online mode I can send characters from the ASR33 to
> >> the computer, but the characters coming back do not print. It works
> >> perfectly in Local mode. I have checked and it is full duplex 20ma, which
> >> matches the setup of my current loop converter and I am using 110bps, 7
> >> data bits, 2 stop bits and Even parity. The ASR33 does not chatter (run
> >> open) when connected to the converter.****
> >> ****
> >> Today I tried sending a break from the PC to the Teletype. It did not
> >> chatter when I sent the break. I verified with a multimeter that the
> >> current goes to zero, so I am definitely sending the break.****
> >> ****
> >> Does this offer any clues?****
> >> ****
> >> Regards****
> >> ****
> >> Rob****
> >> ****
> >> *From:* Alf Fisher [mailto:alf_fisher at tiscali.co.uk<alf_fisher at tiscali.co.uk>
> >> ]
> >> *Sent:* 24 February 2013 21:39
> >> *To:* r.jarratt at computer.org; 'Teletypeparts'; greenkeys at mailman.qth.net
> >> *Subject:* Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33****
> >> ****
> >> Hi Rob,****
> >> I'm sure others will agree but I believe the ASR33 doesn't actually
> >> need a high voltage source as there is a transistor circuit that actually
> >> drives the electromagnet. I reckon 20 volts with a resistor to limit the
> >> current to 20 mA should work. ****
> >> ****
> >> Is it possible with the Westermo, to loop-back the TTY to itself so you
> >> can print what you type? I don't know what is in the converter but another
> >> way may be to bridge the Tx & Rx pins on the Westermo RS232 port (pins 2 &
> >> 3?). It should work the same as being in Local but you are switched to
> >> Line.****
> >> ****
> >> Alf****
> >> ****
> >> ****
> >>
> >> ----- Original Message -----****
> >> *From:* Rob Jarratt <robert.jarratt at ntlworld.com>****
> >> *To:* r.jarratt at computer.org ; 'Teletypeparts' <teletypeparts at aol.com> ;
> >> greenkeys at mailman.qth.net****
> >> *Sent:* Sunday, February 24, 2013 11:55 AM****
> >> *Subject:* Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33***
> >> *
> >> ****
> >> I have not looked at this problem for a week or so but will be looking
> >> again today. To summarise, I can send characters from the Teletype to my
> >> computer successfully, but any characters I send from the computer to the
> >> Teletype do not print out.****
> >> ****
> >> So far I have verified that the ASR33 is wired for 20ma Full Duplex and
> >> that my Westermo converter works, because I can connect up the current loop
> >> interface into a loopback configuration and I get the characters I send on
> >> the RS232 side echoed back. I am using my RS232 port set at 110bits/sec, 7
> >> data bits, 2 stop bits and even parity. The battery test suggested by
> >> Teletypeparts has not worked though. The only things I have yet to check
> >> are:****
> >> ****
> >> 1. Is the mode relay inside the CCU is operating correctly? I used
> >> a multi-meter to test that the contacts were made and broken correctly. It
> >> looks to be making and breaking contacts OK for the most part. One of
> >> the contacts (AM-15) seems a little bent, requiring the relay to close
> >> completely to break the contact. As the bend was such that the contact
> >> might not open correctly, I tried isolating it with some paper, but it
> >> didn’t seem to make any difference. A couple of contact pairs showed shorts
> >> regardless of the relay position, but the relay was fully wired in, so this
> >> might be expected. The constantly shorted pairs are AM-9 with AM-8, and
> >> AM-1 and AM-2. Is there a simple way to test the relay with a battery? I am
> >> not sure what voltage and current it would need.****
> >> 2. The voltage provided by the converter. I am told it needs to be
> >> 80V and some converters do rather less, perhaps 20V. I have a multi-meter,
> >> but in this case I am not sure where to measure the voltage, I have tried
> >> T+ and T- with respect to the converter’s Shield connection and with
> >> respect to the TTY’s earth but I don’t get any more than about 1 volt, this
> >> is whether I am sending characters or not.****
> >> ****
> >> Any ideas?****
> >> ****
> >> Regards****
> >> ****
> >> Rob****
> >> ****
> >> *From:* greenkeys-bounces at mailman.qth.net [
> >> mailto:greenkeys-bounces at mailman.qth.net<greenkeys-bounces at mailman.qth.net>
> >> ] *On Behalf Of *Rob Jarratt
> >> *Sent:* 10 February 2013 23:10
> >> *To:* 'Teletypeparts'; greenkeys at mailman.qth.net
> >> *Subject:* Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33****
> >> ****
> >> I tried a loopback test on my Westermo converter and that worked fine
> >> when looping back from PC back to PC through the current loop. I tried
> >> looping back from the TTY side via the RS232 interface and there was no
> >> echo.****
> >> ****
> >> I then tried the battery test you mentioned and unfortunately that failed
> >> to work too.****
> >> ****
> >> I think the problem must be inside the 33. L****
> >> ****
> >> Regards****
> >> ****
> >> Rob****
> >> ****
> >> *From:* Teletypeparts [mailto:teletypeparts at aol.com<teletypeparts at aol.com>
> >> ]
> >> *Sent:* 10 February 2013 22:28
> >> *To:* r.jarratt at computer.org; greenkeys at mailman.qth.net
> >> *Subject:* Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33****
> >> ****
> >> Rob,****
> >> ****
> >> I have heard of the interfaces being bad but I am afraid I have
> >> exhausted my limited knowledge of interfacing. Some of the guys on
> >> Greenkeys may be able to help you. ****
> >> ****
> >> If you want to eliminate the 33 as a problem completely do the
> >> following:****
> >> ****
> >> Short together 4 and 6 and apply a 9 volt batt to 3 and 7. Again, if
> >> it runs open reverse polarity on 3 and 7. Do the test in Line mode. After
> >> you have the 33 running closed, type a few characters. If they print
> >> OK the trouble is not in the 33. I still dont recommend leaving the batt
> >> on very long. A minute or so. It may not harm anything, but just to be
> >> sure keep the time short. ****
> >> ****
> >> What you have done is make the 33 half duplex (2 wire) and tested it in
> >> line mode. I do that all the time here to check out the 33 in Line mode.
> >> I also use a test generator, but before I had that I used the 9 volt batt
> >> test. ****
> >>
> >> Wayne****
> >>
> >> -----Original Message-----
> >> From: Rob Jarratt <robert.jarratt at ntlworld.com>
> >> To: 'Teletypeparts' <teletypeparts at aol.com>; greenkeys <
> >> greenkeys at mailman.qth.net>
> >> Sent: Sun, Feb 10, 2013 4:28 pm
> >> Subject: RE: [GreenKeys] Current Loop to RS-232 Conversion on ASR33****
> >> I do understand about the echo that is needed to get characters to
> >> print in line mode. I am using a terminal emulator on the PC to receive and
> >> display the characters I type on the ASR33, and I type characters into the
> >> terminal emulator to send them to the ASR33 in the hope they will be
> >> printed. The emulator successfully displays the characters I type into the
> >> ASR33, but the ASR33 does not print the characters I type into the
> >> emulator, despite the Westermo LEDs showing activity which suggests it is
> >> receiving the characters from the emulator and sending them on to the ASR33.
> >> ****
> >> ****
> >> I had to re-read about start bits because I had forgotten about them. I
> >> think start bits are always present, so there is no setting to control
> >> them. So basically, I think I am already using 1 start bit, 7 data bits,
> >> one parity bit and 2 stop bits, but nothing is getting printed. I am using
> >> a line speed of 110 bits/sec, which in this case corresponds to 110 baud
> >> too.****
> >> ****
> >> I suppose the Westermo converter could be faulty and not sending data
> >> out to the ASR33. Unless anyone has any other suggestions I’ll try a
> >> loopback test on the converter to see if it is working.****
> >> ****
> >> Regards****
> >> ****
> >> Rob****
> >> ****
> >> *From:* greenkeys-bounces at mailman.qth.net [
> >> mailto:greenkeys-bounces at mailman.qth.net<greenkeys-bounces at mailman.qth.net?>
> >> ] *On Behalf Of *Teletypeparts
> >> *Sent:* 10 February 2013 18:20
> >> *To:* r.jarratt at computer.org; greenkeys at mailman.qth.net
> >> *Subject:* Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33****
> >> ****
> >> Rob,****
> >> ****
> >> Read on as I put something important below. ****
> >> ****
> >> I guess the voltage doesnt need to be 80 or more. It may run OK with
> >> less. The norm is 20 MA at 120 VDC. ****
> >> ****
> >> I dont know anything about the Westermo, but I know that when you send
> >> to the computer from the 33 the computer needs to be programmed to echo
> >> back to get a copy on the 33. ****
> >> ****
> >> When you type in Local, the print is pretty much instant. When you
> >> type in Line thru the computer you will see a slight delay, not much but
> >> enough to notice. ****
> >> ****
> >> The 33 doesnt care about parity on its receive side, it will print
> >> whatever the bits from 1 to 7 are. The 33 is 110 baud, not sure what that
> >> converts to in computer language. ****
> >> ****
> >> Oh and this is important, you need a START bit which is always a zero
> >> or a space or no current which all terms seem to be interchangeable. The
> >> rest you got correct. Its one start bit, 7 data bits, one parity bit and 2
> >> stop bits. The 33 will run with 1 stop bit, but its normal to give it two
> >> when you can. ****
> >> ****
> >> If you put the START bit in, I bet it will work. ****
> >> ****
> >>
> >> Wayne****
> >> -----Original Message-----
> >> From: Rob Jarratt <robert.jarratt at ntlworld.com>
> >> To: 'Teletypeparts' <teletypeparts at aol.com>; greenkeys <
> >> greenkeys at mailman.qth.net>
> >> Sent: Sun, Feb 10, 2013 5:36 am
> >> Subject: RE: [GreenKeys] Current Loop to RS-232 Conversion on ASR33****
> >> I made some great progress, with one last hurdle to overcome.****
> >> ****
> >> I configured the Westermo to be in active mode (ie supply current) on
> >> both its receive and transmit sides). This cured the problem with the RD
> >> light on the Westermo being on all the time and it stopped the chattering
> >> too.****
> >> ****
> >> I connected it up to a terminal emulator running on my PC. When I
> >> press a key on the ASR33 the corresponding character appears on the
> >> terminal emulator. However, when I try to send characters from the terminal
> >> emulator to the ASR33 nothing happens. I am using 110bps, 7 data bits, even
> >> parity and 2 stop bits.****
> >> ****
> >> As the chattering has stopped, does this mean that the Westermo’s
> >> transmit side is set up correctly now?****
> >> ****
> >> Am I using the right serial port settings?****
> >> ****
> >> Could the Westermo not be outputting the right voltage? It is a 20ma
> >> interface, but the manual does not say anything about the voltage which you
> >> say needs to be 80V or more.****
> >> ****
> >> What else might prevent the characters from being printed out?****
> >> ****
> >> Regards****
> >> ****
> >> Rob****
> >> ****
> >> *From:* Teletypeparts [mailto:teletypeparts at aol.com<teletypeparts at aol.com?>
> >> ]
> >> *Sent:* 09 February 2013 20:30
> >> *To:* r.jarratt at computer.org; greenkeys at mailman.qth.net
> >> *Subject:* Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33****
> >> ****
> >> Rob,****
> >> ****
> >> The 33 should chatter or run open when in Line mode and not connected
> >> to anything. The reading of a short is normal as on 3 and 4 you are
> >> basically looking at a switch, the distributor of the 33. Same reading on
> >> 6 and 7 as I recall. ****
> >> ****
> >> Neither side of the 33 generates any current. The receive wants 20 MA
> >> at 80 volts or more and the send will accept whatever the interface gives
> >> it, usually 12 or 15 volts. ****
> >> ****
> >> A quick test you can do is wire a 9 volt batt to 6 and 7 while in line
> >> mode. You have a 50/50 chance of getting the polarity correct. If still
> >> running open, reverse the leads. The 33 should run closed. Dont leave the
> >> batt connected for a long time. You have now verified the 33 will run
> >> closed in Line mode and you need to proceed with the adapter stuff of which
> >> I know very little. ****
> >> ****
> >> I believe the Send side of the Westmo should be set to active to
> >> generate 20 MA current for 6 and 7 of the 33. ****
> >> ****
> >> Dont know about the Westmo receive side. ****
> >> ****
> >> Hope this helps,****
> >> ****
> >> Wayne****
> >> -----Original Message-----
> >> From: Rob Jarratt <robert.jarratt at ntlworld.com>
> >> To: greenkeys <greenkeys at mailman.qth.net>
> >> Sent: Sat, Feb 9, 2013 7:22 am
> >> Subject: [GreenKeys] Current Loop to RS-232 Conversion on ASR33****
> >> I emailed this list a little while ago about getting my ASR33 to talk
> >> RS-232. I have since sourced a Westermo MA-21 current loop converter.****
> >> I have noticed however, that the ASR33 will “chatter” in line mode
> >> regardless of whether the current loop wires are connected to anything or
> >> not. When I plug it into the Westermo the RD light on the Westermo comes on
> >> even if the ASR33 is disconnected from the mains. The RD light is supposed
> >> to come on when it is receiving data from the line interface (manual here
> >> if you want to see it:
> >> http://www.westermosales.com/pdfs/MA-21manualENGSEDE.pdf), which makes
> >> no sense if the ASR33 is not even connected to the mains.****
> >> I have set both the receive and transmit side of the converter to
> >> passive mode for now (ie they don’t generate the current), but I think the
> >> receive side of the converter will need to be set to be active so that it
> >> generates the current because the drawings of the ASR33 suggest that the
> >> ASR33 receive side generates current but the transmit side does not. In
> >> fact all the switches are set to the factory settings at the moment.****
> >> I tried switching the receive side of the converter to active and when
> >> I switched on the converter (with the ASR33 disconnected from the mains)
> >> the RD light did not come on this time.****
> >> I have also noticed that with the ASR33 disconnected from power the
> >> screw terminal pairs 3&4 and 6&7 appear to be shorted (ie 3 shorted to 4, 6
> >> shorted to 7). I suspect this may be expected but I am not sure.****
> >> I have wired screw terminals 3&4 on the ASR33 to the Receiver side of
> >> the Westemo, and 6&7 to the Transmitter side.****
> >> I wonder if there is a fault in the ASR33, should it chatter in line
> >> mode when it is not connected to anything?****
> >> Which side (if any) of the Westermo should be set to active to
> >> generate current?****
> >> Regards****
> >> Rob****
> >>
> >> ______________________________________________________________****
> >>
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> >>
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