Path: utzoo!attcan!uunet!comp.vuw.ac.nz!virtue!canterbury.ac.nz!phys169
From: phys169@canterbury.ac.nz
Newsgroups: comp.terminals
Subject: Re: Help with setting stop bits in heath-19 (h19)
Message-ID: <1990Oct5.124322.9326@canterbury.ac.nz>
Date: 5 Oct 90 08:24:45 GMT
References: <84209@tut.cis.ohio-state.edu>
Organization: University of Canterbury
Lines: 51

In article <84209@tut.cis.ohio-state.edu>, jxr@dinghy.cis.ohio-state.edu (J Ramanujam) writes:
> I need some help in seeting the number of stop bits on
> a Heathkit-19 (h19) terminal - the "format" used here
> is 8 nits, NO parity bit and 1 stop bit - I am able to
> set 8 nits with no parity bit but not the stop bit.

Don't worry about the stop bit; the terminal will be transmitting
either 1 or 2 stop bits - if it is 2 and the computer expects 1, the
extra bit is simply taken as "idle time" and ignored. Data coming back
from the computer to the terminal might have problems (framing errors),
but usually old terminals default to 1 stop bit if eight data bits are 
selected; I don't have my H-19 manual handy, but from what you say about the
"NO CARRIER" error, my guess is your problem is really one of the
modem lines being disconnected ("Carrier Detect" should be positive
5-12volts).  If there is still a problem with stop bits and you cannot
change the terminal's settings, try setting Parity to MARK or SPACE, and
see if this helps. This applies to any terminal, not just the H-19.

But your main concern should be the wiring between computer & terminal. The
following is the GENERAL ALGORITHM FOR WIRING VDU'S & COMPUTERS:

(1) measure the output of pins 2 & 3 from the computer (pin 7, or the metal
cabinet of the computer is earth); also measure the voltage on these pins
on the terminal. One pin should have a negative voltage (about -10v), the
other very little voltage. If the negative pin on one is 2 and the other is
pin 3, then you need a "1-1" cable, otherwise you need a "null-modem" cable.
If you don't have a multimeter, start by assuming you need a null-modem cable,
and try a 1-1 only if that fails.

(2) for a null-modem cable, connect pin 2 of one plug to pin 3 of the other,
and vica versa. Connect pin 20 of one to both pins 6 & 8 of the other, and vica
versa. Connect pin 7 of one to pin 7 of the other. You might like to connect
pin 1 to pin 7 at one or both ends as well (they are earth pins). If you have
enough wires left in your cable, connect pin 4 of one to pin 5 of the other,
and vica versa, or just connect pin 4 to its local pin 5 - thus saving 2 wires.
When everything is connected, you should get -10v (roughly) on pins 2 & 3, +10v
on pins 4,5,6,8 and 20, and pins 1 & 7 should be connected to earth (0v). If
this doesn't work, or if you know the computer doesn't have "full modem" lines,
connect pins 6,8 and 20 together at each plug, and 4 & 5 together at each plug,
so there are only three wires between the VDU & computer (earth, TxD and RxD);
You must use XON-XOFF handshaking in this case.

(3) for a 1-1 cable, simply connect pin 1 to pin 1 of the other connector, pin
2 to pin 2 of the other, etc, until pins 1,2,3,4,5,6,7,8,20 and 22 are all
connected. If this doesn't work, again try linking pin 4 to its local pin 5
instead of the remote pin 4, and pins 6,8 and 20 together instead of linked to
the other equipment. 

Hope this helps,
Mark Aitchison, Physics, University of Canterbury, New Zealand.
(M.Aitchison@canterbury.ac.nz)