80-Bus News

The following article(s) if this prose is worthy of print, will attempt to describe the ins and outs (ups and downs) of getting that very expensive printer PRINTING. Although specific references apply to the MX80 type III, much is applicable to the whole MX-range. Since the interface is a standard ‘Centronics type’, the general principle applies to any number of printers. I refuse to class that race of tanks dressed up as printers (you know… 5 bit code etc.) as printers. By the way, does any one want a slightly footmarked Creed 444? Advertising over – Included will be notes on how to patch into NAS-PEN, NAS-DIS and ZEAP (if it isn’t already obvious) and a listing of a fairly comprehensive relocatable routine to set up and drive the printer through the on board PIO. Later on for those with the MX80 types II or III (and a larger overdraft than everyone else), use of the HI-RES graphic facilities is described. These can be used to define your own characters and with suitable software.... produce a dot for dot dump of the Nascom screen. Do I hear cries of ‘Cor – What a cop out’? Well you can take it all back because a listing of such a program will be given. With luck, it will not only provide a simple screen dump but also true/​inverted and half/​normal/​double width images of any defined screen window. (This guy is just unbelievable! – Ed.)

Epson Interface.

But first the basic printer interface and its driving software. The rightmost columns of Table 1 show the pin connections of the Epson interface. All signals are (naturally) TTL compatible. Synchronisation is achieved by the STROBE signal and handshaking provided by either ACKNLG or BUSY. I have chosen to use the BUSY line, but for no particular reason. Data transfer is achieved by waiting for the printer to be ‘NOT BUSY’, applying the data, waiting for it to stablise and then asserting STROBE for a minimum of 0.5 microsec. Apart from ACKNLG, the only other signals (on the printer I/F) not used are SLCT IN and SLCT. The function of these (to select the printer/​tell you it is selected respectively) was disabled using the Epson’s internal DIL switches. This is OK as I don’t see me operating a bank of MX’s fram my Nascom – not this year at least!

DIL Switches.

The internal DIL switches definitely deserve a mention as they allow you to set up many of the programmable functions immediately en power up. Things like character size, form length, line spacing and even whether or not your zero has a slash across it can all be set.

The Electric String.

The assignment of the PIO ports is shown by diagram 1 and the actual connections made by the cable is shown by the middle columns of table 1. The Epson manual tells you to use twisted pair cable and the return earth signals. Twisted cable is not easy to get hold of and shouldn’t be necessary so long as the