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Serial Communications on the PC Search  Prev Next 

The first step is to connect your PC to the remote computer using a serial cable. The only actual Wyse terminals I've seen, have 25-way, female, D-type connectors on the back:

Diagramatic rear-view of Wyse-55 Terminal

Modern PCs have one 9-way, male D-type:

Connectors on modern PC

While older PCs often have one 25-way, male D-type:

Serial connectors on old PC

If you have an existing serial cable, it is possible to buy plugin adapters that will convert from a 25-way, male D-type plug into a 9-way, female D-type plug suitable for most PCs:

9way-to-25way adapter and Gender-Changer

Your friendly local computer store is a good place to buy such adapters from.

Note: sometimes a combination of a 'gender changer' and a '25-way into 9-way converter' will be required.

The alternative is to make (or buy) a suitable serial cable. The connections for the PC end should allow the use of hardware handshaking, preferably using the RTS/CTS lines. If you are going to be logging into a Unix box, the DTR line usually needs connecting so that the remote computer knows that a terminal is connected and switched on.

For completeness, here are two diagrams which show the mapping between a 25-way and a 9-way RS232 D-type connector, and the wiring for an RS232 serial cable to connect two PCs together so that hardware-handshaking works:

Mapping of 9-way and 25-way RS232 D-type connector PC-to-PC wiring diagram

The second diagram uses pin numbers for a 25-way D-type, and these pin numbers and signal names match those of a Wyse Terminal (the PC and most terminals are DTE devices).


Getting serial links working correctly can be fraught with difficultly and without the use of serial line monitoring gadgets or at least a multi-meter there can often be too many unknowns for a novice.

I like to start from a known state, so I want to see a working terminal session on the cable I am going to use before wasting a lot of time.

The settings for baud-rate, parity, data bits, stop-bits, and handshaking can be read from the working terminal configuration:
  • On a Wyse-60 the settings can be inspected by pressing a SHIFT key with either the SETUP, RESET, SYS-REQ or SELECT keys - dependent on the keyboard type.
    (F10 to exit setup)
  • On a Wyse-55 the settings can be inspected by pressing SHIFT SETUP, CTRL SETUP, F3, SHIFT SELECT, or CTRL SELECT - dependent on the keyboard type.
    (F12 to exit setup)
Both terminals usually use the 'modem' port for communicating with the remote computer and these settings are under COMM on the setup menu. It is worth exploring the other settings here, but don't change anything, just EXIT when leaving setup. You will notice that the Wise Terminal program settings screens contain very similar settings and options.

All you have to do then, is use a trusty gender-changer/ 25way into 9way adapter combination and get the serial port working on the PC.

Problems I have encountered include:
  • PC serial port not actually connected internally.
  • Serial port hardware blown.
  • Dislodged pins in D-type.
  • Faulty or swapped ribbon cable connectors in PC.
  • Serial cables with invisibly fractured cores.
  • Gender changers or 25<->9 way adapters with signal paths missing/ faulty.
  • The COM1 and COM2 connectors being swapped.
  • Serial ports disabled to free up interrupts on the PC for e.g. an internal modem.
  • Misleading information on the remote computer connections, settings, requirements etc.



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