Retro-tech HP-25 calculator clones using Z80
| 
| 
|
2021-01-01
Time for something new! The VFD HP-25 is cool and all, but I've lusted after an HP-97 most of my life, plus I love nixie tubes! Starting to think about a nixie-display HP-97 emulator. Probably no card reader, but a small printer is certainly doable. Inspiration from Oliver De Smet (archived elswhere in this repository just in case):
- https://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv020.cgi?read=204526
- https://sites.google.com/site/olivier2smet2/hp_projects/hp97
2020-10-10
I gave a talk at the HPCC 2020 conference on these calculators. You can see my slides here: http://www.hpcc.org/conferences/HPCC2020/HPCC2020_04_Retro_25_revC.pdf
Built a new version with VFD display tubes!
hardware has the design files for the CPU and keyboard/display boards
firmware/bootloaderhas a small serial/flash bootloader which should be programmed at $0000firmware/calchas the main calculator operating firmwarefirmware/umonhas a simple Z80 monitor I wrote for debuggingfirmware/basichas a hacked version of MS BASIC (4K integer version from 1978)utilhas some utility software, including: firmware loader, program loader, stack/register clip utility, simple assembler for HP-25 programs, and some template and example programs
The hardware consists of two boards, a CPU board and an LED+display board.
- D2 in the reset circuit - silkscreen is backwards
- U1 pin 11 must be wired to J17 pin 11
- BUSRQ should be tied high or pulled up. Solder a 1k resistor (or just a wire) from the Z80 (U3) pin 25 to +5V
Also, recommend to cut the trace to nWE on the EEPROM (U4, pin 27) and wire from pin 27 to pin 28. This disables writing to the EEPROM. Not essential, but I recommend programming the EEPROM separately in a programmer. Rogue code can easily wear out the EEPROM (as I found the hard way!) if writing is enabled. You have been warned.
The memory map is very simple:
EEPROM | 0000-7FFF
RAM | 8000-FFFF
There are six decoded I/O ports:
| port | name | bits | description |
|---|---|---|---|
| 00 | KB (write only) | bit 0 | KB column 1 |
| " | " | bit 1 | KB column 2 |
| " | " | bit 2 | KB column 3 |
| " | " | bit 3 | KB column 4 |
| " | " | bit 4 | KB column 5 and switches |
| " | " | bit 5 | -not used- |
| " | " | bit 6 | LED on CPU board |
| " | " | bit 7 | Serial output |
| 40 | Digits 0-7 | bits 0-7 | ICM7218 display data |
| 41 | Digits 0-7 | bits 0-7 | ICM7218 control data |
| 80 | KB (read only) | bit 0 | KB row 1 |
| " | " | bit 1 | KB row 2 |
| " | " | bit 2 | KB row 3 |
| " | " | bit 3 | KB row 4 |
| " | " | bit 4 | KB row 5 |
| " | " | bit 5 | KB row 6 |
| " | " | bit 6 | KB row 7 |
| " | " | bit 7 | Serial input |
| c0 | Digits 8-11 | bits 0-7 | ICM7218 display data |
| c1 | Digits 8-11 | bits 0-7 | ICM7218 control data |
All ports except 80 are write-only; port 80 is read-only.
A bit-banged serial port using an FTDI USB adapter is provided
as bit 7 of ports 00 and 80. Note that these ports share
keyboard scanning functions, so the code must be carefully written
if both functions are used simultaneously.
There are no interrupts.
See firmware/calc for calculator operating program
See util for assembler and loader utilities
React
Typescript
Django
Laravel
Facebook
Microsoft
Google
Alibaba
D3
Tencent