[GreenKeys] Current Loop to RS-232 Conversion on ASR33

Mon Mar 18 23:05:37 EDT 2013

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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