Nascom News­let­ter

1. Introduction

Nascom microcomputers are designed to allow the use of a wide range of different printers. The procedures used to connect these different printers depend on the individual printer, but can generally be divided into three groups.

1. Serial printers without handshake. Most slower printers fitted with a serial interface to RS232, V24 or 20mA current loop standards can run continuously at their data transfer speed – usually 300 baud (equivalent to 30 characters per second). Both Nascom 2 and Nascom 3 have a suitable serial interface fitted as standard.

2. Faster serial printers running at a data transfer rate of 1200 baud (equivalent to 120 characters per second) can accept coded characters at this speed, but cannot continuously print this fast. Instead they have an internal memory in which the data is stored prior to printing. If the computer continues to output characters at full speed the printer memory fills, and if the printer could not tell the computer to wait some data would be lost. Such printers are therefore normally fitted with an additional connection, called the ‘handshake’line, which is connected to the computer to notify the computer when the printer memory is full. A connection is available on Nascom 2 and 3 for this purpose, although an additional software routine is required to support it.

3. Parallel interface. In this case instead of the code for each character being sent serially along one wire a separate wire is used for each code bit of the character. The interface is frequently referred to as a ‘Centronics’ interface, snce it has been widely used by one of the largest American specialist printer manufacturers, Centronics. The uncommitted parallel ports from the PIO fitted as standard to the Nascom 2 and 3 can be used to drive such printers.

This application note describes in detail how to use any of these types of printer with a Nascom 2 or 3 computer. Normally your dealer will be able to supply the correct connecting cable, but for those wishing to make up their own full details of the connections required are given. If you have a suitable cable then you should concentrate on the software details. These software procedures are very easy to implement, although the extensive description of all possible methods of use given in thus note may make them appear rather more difficult than is actually the case.

2. Printer connections

2.1 Serial printers without handshake

Your dealer will normally supply an appropriate cable and