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HP35 ROM HP calculator chip sets

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On this page I will describe the evolution in calculator chips used by HP. For every new generation of calculators the number of chips is reduced by increasing functionality in one chip. In the current calculators the number of chips is reduced to only one.

 

The Classic series

This series used a multi chip CPU. The block diagram below shows the separate chips.
This figure is copied from HP patent US 4,001,569.

Block digram Classic series

The processor function is divided over two chips, a Control & Timing circuit (CTC) and an Arithmetic & Register control chip (ARC). These chips together with the ROM chips and the clock driver are build on a single printed circuit board. This printed circuit board also contains a discrete build power supply and a power-on detection circuit. The main PCB contains the keyboard, LED display modules and the anode and cathode driver ic's for the LED displays.

The major difference between the different Classic models is the number and content of the ROM chips. The number of ROM ic's differs from 3 for the HP-35 up to 7 for the HP-80. The programmable models also have RAM ic's to store the program.

HP55_pcb
Main printed circuit board of the HP-45
Main printed circuit board of the HP-55

Most models use the same chip for the CTC, ARC and RAM ic's. The ROMS which contain the software are unique for each model. An overview of these chips can be found on the web site of Eric Smith. Below an overview of the chips I found up to now in the Classic models of my collection.

Model
Anode-driver
Cathode-driver
Clock-driver
Control&Timing
Arithm&Reg
ROM
RAM
Card-reader
HP35
1820-0853
1820-1029
1820-0854
1820-0855
1820-0849
1818-0011
1820-0848
1818-0006
1818-0017
1818-0020
1818-0023
1818-0024
1818-0025
1818-0026
1818-0028
 
HP45
1820-1029
1820-1226
1820-0855
1820-1128
1818-0078
1820-1169
1818-0057
1818-0082
1820-0993
 
HP55
1820-1029
1820-1226
1820-1128
1818-0078
1818-0079
1820-1169
1818-0118
1818-0119
1818-0120
1820-1393
 
HP65
1820-1029
1820-1226
1818-0073
1818-0074
1818-0075
 
HP67
1818-0268
1820-1749
1820-2530
1818-0231
1818-0232
1818-0550
1818-0551
1820-1751
1826-0322
1858-0050
HP70
 
HP80
1820-1029
1820-1061
1820-1127
1818-0078
1820-0848
1813-0024
 

A very nice saga about the HP-35 can be found on the web site of Jacques Laporte.

 

The Woodstock series

A block diagram of a Woodstock model is given below. This drawing is copied from the HP Journal 11-1975.

Woodstack block diagram

For the woodstock models the CTC, ARC and power on functionality is combined into one chip, the ACT, Arithmetic Control and Timing. The ROM is added to the Anode driver chip. Dependent on the model additional separate ROMs are used.

HP22_pcb
This picture shows the chips on the lower side of the HP-22 PCB. The anode and cathode drivers are location on the top, below the LED display.

The power supply is still build from discrete components.

Most models use the same chip for the ACT, Cathode driver and RAM. The ROMS which contain the software are unique for each model. Below an overview of the chips I found up to now in the Woodstock models of my collection.

Model
ROM + Anode-driver
Cathode-driver
ACT
ROM
RAM
POR
HP21
1818-0129
1820-1382
1820-1741
 
HP22
1818-0163
1820-1382
1820-1523
1818-0164
1820-1564
 
HP25
1820-0168
1820-1382
1820-1523
1818-0154
1820-1564
 
HP29C
1818-0431
1820-1382
1820-1396
1818-0376
1818-0377
1818-0379
3061-0469
1818-1983

 

The Topcat Series

The next figure shows the block diagram of the HP-97 calculator.

HP97 Schematic

 

The Sting Series

The Sting model HP-10 has a one chip CPU, RAM, ROM and display/printer driver chip.

The HP-19C model has almost the same chipset as the HP-29C Woodstock model except for an additional printer driver circuit.

 

The Spice Series

The models of the Spice series only contain a large processor chip and up to three small ROM chips. The processor takes care of the keyboard scanning, computing and the control of the LED display.

HP32E chipset

This photo shows the chips inside the HP-32E calculator. For this model the chips were not soldered on a PCB but pressed on the PCB. See also here for more information about the HP-32E.

This photo shows that there is space for 3 ROM chips, but this model only uses two.

The print on top contains the discrete build power supply.

 

The Coconut series

The first series Coconut calculators had a separate print with the power supply, controller and memory chips. This series is known as the full nut series.

HP41CV_inside_4

The later models have all electronics integrated into one chip, mounted on the keyboard PCB. This series is known as the half nut series.

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HP chip set related links:

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