HP41C with Rp Pico attached

[brouhaha]

(03-15-2024 11:16 AM)floppy Wrote:  Sniffing then extending an HP12C bus would make it interacting with the external world?

The bus is the same, though the LCD control is different. There are two registers at addresses 0x09 and 0x0a, which hold the bimap for the 100 software-controllable segments of the display, 50 bits per register. See "synthetic Methods on the HP-15C" by Allyn Tennant, though note that on the 10C the segment mapping is different.

There are also the same display off and display toggle instructions of the 41C family, but in addition, an instruction 0x030 that sets the display to flashing mode. (The display off instruction exits the flashing state.) The display flash timing is independent of the CPU, and in particular, do not start/stop or change the phase of the display blink timer based on any CPU instructions, including the display control instructions. If you do, you'll end up with incorrect displays of "running", either blank almost all the time, or active almost all the time without flashing.

For general interfacing or for duplicating the display, fundamentally you need the phase 1, phase 2, sync, ISA, and DATA lines. I've identified some signals on the 1LF5-0301 CPU used in early Voyagers, but not the DATA line. DATA should probably be the pin between GND and SYNC, but I haven't verified that. The 1LF5-0301 is in a modified 44-pin QFP. Many pins are missing, and some pins in the middle of sides exist but do not have the gull-wing forming, so are not connected to the PCB.

I haven't verified that the later 1LM2 has the same pinout as the 1LF5, but it's reasonably likely that it does.

AFAIK, the single-chip versions (1LQ9, 1RR2, 2AF1) don't have the external bus active, except on the 15C. There should be a factory test mode that enables the bus, but it is not publicly known how to activate that.