A new old bug in the printer ROM?

[brouhaha]

(10-23-2023 08:11 AM)Tinue Wrote:  So I am still wondering why Swiss Micros wrote their own code for the remapping, instead of merely adapting the IR output part of the 82242A to suit the hardware of the DM41X.

None of the Swiss Micros calculators contain an 82242A.

Using the 82143A's ROM and doing code translation is an obvious way to get the most important functionality. Richard Ottosen and I did that on our prototype calculators starting in 2007.

An alternative would be to use the 82160A printer ROM, but that would be much more complicated for not much benefit.

Quote:Then again: The ROM seems to be undocumented any possibly too hard to understand and modify.

There's a lot more in the 82242A than ROM, but yes, it is also the case that the 82242A ROM code is difficult to understand. I was able to reverse-engineer how HP's PIK (printer interface and keyboard) chip for the 19C/91/92/95C/97 worked from first principles, and also how the CRC (card reader control) chip of the 67/97 worked from first principles, the latter with some assistance from Jacqes Laporte. I looked at the 82242A ROM, and couldn't really begin to make heads or tails of it, aside from the 41 user code portion that is about the same as that in the 82143A and 82160A ROMs. Admittedly I didn't spend a huge amount of time on it. If I were to attack the problem now, I'd wire up an extender to run the 82242A physically at a distance from the calculator port, and monitor the Nut bus lines (clock, SYNC, ISA, DATA, possibly flag) while performing specific printing operations.

The interface inside the 82242A between the HP-41C bus and the infrared LED is totally unknown. The Nut processor is far to slow to modulate the 32.768 kHz IR carrier directly. Aside from that, it is necessary to pace the output in a fairly complicated way, modeling the expected worst-case buffer level in the printer; see the HP Journal article on the 82240A printer for details. There's almost certainly a custom interface chip, and there may or may not be a microcontroller, either as part of that chip or separate from it..