I've been playing with the HP-45 and HP-55 simulators---very
interesting! It turns out there are some errors in the assembly code as transcribed from the listings in the patents:

hp45.asm:

---------

99c99

<       if a[x] >= 1

---

>       if a[xs] >= 1

hp55.asm:

---------

67c67

< ofl:  delayed select rom 3

---

> ofl:  delayed select rom 5

1601c1601

< ent14:        c -> a[x]

---

> ent14:        0 -> a[x]

2012c2012

<       c + 1 -> c[w]

---

>       c + c -> c[w]

2025c2025

<       c + 1 -> c[w]

---

>       c + c -> c[w]

3115,3116c3115,3116

< out1: c - 1 -> c[xs]

< out2: c - 1 -> c[xs]

---

> out1: c - 1 -> c[x]

> out2: c - 1 -> c[x]

They were found by hacking up an OCR to look at the '1's and '.'s in the patent TIFFs, so these are probably all the mistakes.

The HP-55 now works under casmsim, at least in ordinary "run" mode. I don't know how to emulate the timer-program-run switch, though. Something to do with S3 or S8, maybe, but exactly what is not clear from the code (which could do with a few comments).

A modified xio.c to display the HP-55 keyboard is available here, along with revised hp45.asm and hp55.asm:

http://www.pmonta.com/calculators

Cheers,
Peter Monta