[GreenKeys] TeleType Model 33 Not Sending Some Control Characters Correctly

[Robert Jarratt]

Hello Mike,

 

You are right it is parity, for some reason I had thought that letters A and B had a different number of high bits, but they don’t.

 

You are also right, that parity seems to be being put into bit 7 rather than bit 8. Both CTRL-C and letter C transmit a hex 43 value.  I have taken pictures of the left side of the keyboard, tell me if they look OK. They are posted here: http://sdrv.ms/1dOUMwT.

 

Regards

 

Rob

From: greenkeys-bounces at mailman.qth.net [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Mike Douglas
Sent: 27 October 2013 02:06
To: greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] TeleType Model 33 Not Sending Some Control Characters Correctly

 

Robert,

 

Sorry it took so long for me to jump in - I've been out of pocket for a while.

 

If you have levers and contact wires on the left side of the keyboard that move with the control and shift keys, then yes, you have a parity keyboard. Also, your problem is clearly correlated to parity.

 

Note that every character you're having problems with has the parity bit set when control is not pressed. The control key is supposed to open the bit 7 path to make it a zero and then invert bit 8, the parity bit. It sounds like the contact wires on the left side may not be arranged exactly right in the plastic sliders and somehow the parity bit is ending up in bit 7. Can you get a really clear close-up photo of the left side contact wires for me? Can you tell me what is received for Bit 8 when you press a C and a Ctrl-C, for example?

 

Mike


On Oct 26, 2013, at 4:24 PM, "Robert Jarratt" <robert.jarratt at ntlworld.com> wrote:

I have had two replies on this and finally got a chance to look at it today. I was asked if I had moved the machine, while the answer is yes, the problem had started before I moved it.

 

I have been looking at the manual and at my machine and I am slightly confused. I believe I have a parity keyboard. The manual 574-121-100TC in Fig. 10 shows a set of contact wires at the left and the right that are operated by the CTRL key.

 

However, on my keyboard there are no contact wires on the right (as you look from the front) operated by the CTRL key, nor is there room for any; it doesn’t look as if anything is missing or broken either. In fact if that was the case then it would not work with any letter keys at all, but the reality is that it works correctly for some keys but not all of them.

 

>From what I can see, the operation of the CTRL key is always the same. It changes the contact wires on the left of the keyboard regardless of what letter key I press at the same time, and on the right it has no effect at all on the contact wires. So I don’t get why sometimes it seems to work and other times it doesn’t.

 

Regards

 

Rob

 

From: Robert Jarratt [mailto:robert.jarratt at ntlworld.com] 
Sent: 21 October 2013 22:15
To: greenkeys at mailman.qth.net
Subject: TeleType Model 33 Not Sending Some Control Characters Correctly

 

My Model 33 had been working perfectly. But for some reason it has started not to send some characters to the computer correctly.

 

For some reason CTRL-C (ASCII 3) is sent as “C” (ASCII 43 in hex). For what I need it for this is disastrous because it is the character I need to send to start the login sequence on the simulated computer that I need it to log in to. I have checked all the CTRL keys, the ones that don’t work are CTRL-C, CTRL-E, CTRL-F, CTRL-I, CTRL-J, CTRL-L, CTRL-O, CTRL-Q,  CTRL-R, CTRL-T, CTRL-W, CTRL-X, in each case hex 40 is added (ie bit 7 is set). It does not even seem to be a parity issue because contiguous characters are sent incorrectly.

 

Ordinary letters are sent correctly.

 

Any ideas where to start looking?

 

Regards

 

Rob

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