HP82240B Printer simulation 1.18

[Christoph Giesselink]

There's a bigger update in the HP82143A mode inside the HP82240B simulation. This has an influence on older implementations using this mode.

Mike detected a larger bug when trying the test print in the HP82143A Service ROM.

The test result of HP82240B 1.17

   

has less or nothing todo with the expected result printed in the Service ROM manual and generated with 1.18

   

The reason is a very special handling of printer internals, especially the handling of the 44 byte character input buffer. But also some assumptions about internal behavior had been wrong. So bugs and these wrong assumptions are also reponsible for the wrong output.

So the assumption that an EOL (end of line) character E0 or E8 clear the SCO (Special Column Output) bit in the printer status register was wrong. To get the test print working, this behavior changed, an EOL character does not clear the SCO bit any more. But this caused a change in applications using this printer mode. This fix in the printer implementation was necessary for a proper simulation, so no way back to the old behavior.

One of the design problems of the HP82143A printer simulation is, because of the HP82240B origin, that the printer simulation has no return channel to return the content of the printer status register to the NUT CPU. But for proper printer handling it's an essential that the NUT CPU gets the correct status of the EOL, TEO, DWM, SCO and LCA bit! The solution is, that the sending application using a copy of the printer status register updated by the characters send to the printer.

So the implementation inside V41 R9L cleared the SCO bit in the printer status register copy when sending an EOL character. This was the printer simulation behavior of 1.17. But with the changed behavior in v1.18 the PRPLOT, with the WIGGLE example of the printer manual, printing output fails.

When using actual V41 R9M in connection with HP2240B v1.18 everything is working fine again. This version does not clear the SCO bit in the status register copy when sending an EOL character. So be aware, when using the 1.18 printer simulation software, that you use the latest transmit software.

So when PRPLOT fails, look for the latest software revision of the transmitter software or make a change request to the author of the transmitter software.