Interfacing the EPSON MX80.
by Big H
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.)
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
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