Great, does this sound correct?
In the next piece I will describe how I connected the eighth printer bit to a printer. The fact that the standard printer only sends 7 bits irritated me immensely, it is not possible to use the full character set of the printer without special tricks.
Now I had read a piece about an active bit using the CSS bit of the PlA but for this the software of the printer routine has to be adjusted to make it possible to send a full character to the printer. This is therefore not such a good solution.
The problem is actually that all bits of the A-port are occupied, bit 7 of the A-port is needed to detect the BUSY.
If you look at the printer routine, it appears that there is not a single byte sent to the printer (VIA), but that only 7 bits come out at the output of the VIA, because only the lower 7 bits (B0-B6) are programmed as output.
So what is the solution 7. The eighth bit that is sent to the printer must be held via a latch (D-flip-tlop) when writing in the data register of the A-port.
This can be realized with 2 ICs (see enclosed diagram). In this diagram a 74LS74 D-FF is used, but with other types of D-FFs that you have available, it should also work. For decoding address #B801 a 74LS138 is used, but here too it applies that it should also be possible with other ICs; for the ICs indicated here I have made a print.
The intention is that this print is attached to the VIA with spaghetti wiring, or glued elsewhere in the cabinet.
Now it is possible to print the complete characteristics of the printer without software changes,
For example:
10 P.%2
20 FOR X=#20 to #FF
30 P.%X
40 NEXT X
50 P.%3
60 END
RUN
Nico van Rooijen
Region Zeeland.
Statistics: Posted by matalog — Tue Mar 11, 2025 12:38 pm