jxr@dinghy.cis.ohio-state.edu (J Ramanujam) (09/30/90)
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. Using the commands on the modem, I can figure out that it is indeed 8 bits with no parity but I am unable to figure out the number of stop bits. As it stands, I am not able to connect to the system (all I get is NO CARRIER) I would like to know how to set/determine the number of stop bits. Thank you very much. - Ramanujam
phys169@canterbury.ac.nz (10/05/90)
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)