The SL55 comes with a 9pin male serial connector which allows interfacing to a computer to download software and data. Most PC's also have a similar 9w male connector fitted and many may have two. Older machines might have a 25w serial connector. In all cases the serial connector on the PC is a male. If you have a female 25w connector, its the printer port and uses different voltage. This cannot be used.

In order to connect the two, you need a crossover cable The signalling consists of a varying voltage transmitted on one pin and received on another, so transmit at one end must go to receive at the other. Sometimes this is called a null modem cable. When serial terminals were commonplace, they were designed to be connected to a modem. To connect two together without using them required ... a null modem cable. However, that cable also used other connection pins that we do not need for our purposes.

Unless you can buy a 9way female to female crossover cable ready made, you need to buy two D shells, two shrouds (the covers) and a short length of cable.

In the UK a suitable supplier is Maplin

Its also possible to get 9w D connectors in a cover fitted with a RJ11 telephone connector, providing you ensure that the transmit and receive signals are crossed over, they work fine and there is no need to solder. Crimp sonnectors are another alternative but may require special tools.

The actual cable and length is not critical as the signalling is pretty slow, robust and immune to interference

A suitable 9w D connector mounted in its cover

Wiring diagram showing pins crossed over and the common return on pin 5