HP 19B teardown part 1

[brouhaha]

Good news:

G1) It turns out that Travis Goodspeed has already decapped and photomicrographed an HP Lewis chip from a 28S. This is the same chip, with different ROM contents, as is used in the 19B and 19BII. He was kind enough to share the mulitple gigabytes of raw images with me.

Bad news:

B1) It appears that the process geometry is probably too fine to support optical ROM extraction such as Peter Monta did with the HP-35 ROMs.

More good news:

G2) I don't need to finish setting up my decap lab, at least for this project. I may still want to do it for other chips.

G3) I have another plan for how to do it electrically. Extracting the contents of the slave Lewis should be easy, as it has to provide its ROM contents over an external bus to the master Lewis. Having half of the contents isn't useful in and of itself, but once it's done I should be able to cut traces and insert an FPGA-based Saturn ROM emulator between the two Lewis chips. As long as I can indentify some key sequence that results in a transfer of execution to the slave ROM, I should be able to inject code that can dump the master ROM.

As this point I think it will be best to experiment with an HP-28S to prove that this can be done before moving on to the 19B and 19BII; since the HP-28S code is already known, that will make it much easier to experiment with.

If anyone has a spare HP-28S that they're willing to sacrifice in the name of science, please let me know.