HP HPIB chips

A week or so ago there were a few messages about the HP 'Medusa' HPIB chip. While looking for indormation on the custom chips in the HP printer I'm working on from time to time, I cam across some comments that might be applicable. The HPIB interface chip in the HP2531 printer is called 'Phi'. According to HP Jorunal July 1978, it is a silicon-on-saphire CMOS device. It's pacakaged in a 48 'pin' leadless ceramic package, and has the number 1AA6-6004 The Medusa, packaged in a 48 pin DIL package, seems to be a closely related device. The pinot is in the same order, for example. This probably explains the rather curious numbering of the data bus pins on the Medusa (D0, D1, and D8-D15, with D15 as the LSB). The best reference I've found so far on this is the reference manual for the HP12009A HPIB interface for HP1000 machines. It's on http://www.hpmusuem,net. THe earlier version of the manual there covers the Phi-based board, the later version the Medusa-based one. They are very similar.. -tony