You will now be able to get hard copy of machine code tabulations, Basic listings,
and source and object code from assemblers and disassemblers. If you use the
printer with Nas-Dis you will come across a strange problem – the machine goes into doubleprint
mode. The reason for this is that after accepting the user options Nas-Dis uses an
ESCAPE (£1B) to get to the beginning of a line, and then prompt “Go?”. Unfortunately the
printer interprets ESCAPE/G as an instruction to double print. The only cures are to
modify Nas-Dis (for example, change to a lower case g), or to use a special printer output
routine for Nas-Dis which ignores ESCAPE/G.
If you try to use the pixel set in the Epson you will find that it is not
compatible with the Nascom pixels; in fact, it is the TRS 80 pixel set, using characters £80 –
£BF or £A0 – £DF (switch selectable). The following section of code carries out the
necessary conversion. The effect of each step in the process is listed on the right. An X
indicates that the value is not a copy of a specific original bit.
|Operation||Current location of|
|Carry Flag||Zero Flag|
|JR NC, ANDA|
|JR Z, RES6|
|SET 7, A||22130765||4||2|
|RES6||RES 6, A||2X130765||4||2|
|JR NC, RRCA|
|SET 6, A||24130765||4||2|
This completes the bit. manipulation; SUB £20 now shifts the characters to £A0 – £DF,
SUB £40 converts them to £80 – £BF.
The graphics ROM in the Epson also contains 64 Japanese characters, which can
be accessed when pin 7 of DIP switch 1, at the back of the printer PCB, is set to ON. These
characters are coincident with the pixels. If you send control code ESCAPE/5 (i.e., £1B
£35 in hex., 27 53 in decimal) subsequent characters in the graphics range will produce the
Japanese set; ESCAPE/4 selects the pixel set. Now, you may not want to print in
Japanese, but a bit of research into the software inside the machine shows that you could
easily reprogram these 64 characters to your own design.
At a first glance at the beautifully made P.C.B. there appear to be some chips
missing. There are three 24 pin sockets near the back edge of the board labelled 2716, but
only one of these contains a chip, which is a 2332! However, this 4K ROM can be
removed and replaced by two 2716s without any modifications to the board.