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HP 45 Internals

Posted by Tony Duell (UK) on 18 Sept 2003, 9:18 p.m.

Mechanical construction (and architecture) very similar to HP35 (see 
previous notes). 2 PCBs, keyboard and display on upper PCB, CPU and ROMs 
on lower PCB. Connections between PCBs by 25 pins (same signals as HP35).

Keyboard/display PCB --------------------

This has an 00035- part number, and seems to be electically identical to the board in an HP35. The 2 chips have different numbers :

Anode driver : 1820-1029 Cathode driver : 1820-1226

but seem electically very similar to the chips in an HP35. Same pinouts (so see previous notes again).

Logic PCB ---------

The 2 transistors and the transformer form a power supply giving the same 3 voltages (for the same purposes) as the HP35. There is no discrete component reset circuit, though (see below for what replaced it).

2 of the chips :

Control and Timing : 1818-0078 Arithmetic and Registers : 1820-1169

have the same pinout as the corresponding chips on the HP35 logic PCB. Presumably they have different instruction sets, though.

This leaves 4 more chips :

1820-1128 Clock driver and init ------- Init --| U |-- Init C --| |-- Phi_2 In --| |-- Phi_2 Out Gnd --| |-- Gnd --| |-- Vgg --| |-- Vss --| |-- Phi_1 In --| |-- Phi_1 Out -------

This replaces the 8 pin clock driver of the HP35 and most of the discrete components in the reset circuit. The signals are :

Phi_n In : 2 phase clock inputs from anode driver (at 'bipolar' levels) Phi_n Out (called Phi_n on other logic board chips) : 2 phase clock outputs to rest of CPU Init : Reset output to C&T and ROMs Init C : 2.2uF capacitor from here to ground -- reset timing capacitor. This is the only component in the HP35 reset circuit that couldn't be put on the chip.

1818-0057, 1818-0082 : ROMs

Similar to the ROMs in the HP35, but presumably higher capacity. Now packaged in 16 pin DIL (ceramic) packages. The signals are the same as the HP35 ROM interface, and the pinout is :

------- Vss --| U |-- --| |-- IA --| |-- WS Gnd --| |-- Init --| |-- Phi_1 IS --| |-- Vgg Sync --| |-- Phi_2 --| |-- -------

See the HP35 notes for signal descriptions

1820-0993 RAM This connects to the (unused in the HP35) data pin on the A&R chip and transfers data to/from the arithmetic registers.

The pinout is : ------- Vss --| U |-- IS Gnd --| |-- Gnd --| |-- Data Gnd --| |-- Phi_2 Gnd --| |-- Phi_1 Gnd --| |-- Vgg Gnd --| |-- Gnd --| |-- RCD -------

Data : Data to/from A&R chip Phi_n : 2 phase clock inputs IS : ROM output (InStruction) line, used to address RAM. RCD : Reset Cathode Driver signal from A&R, used to define start of a word.

Testpoints ; There are 12 testpoints on the edge of the CPU board, in the same position and carrying the same signals as on the HP35. For reference, the signals are :

o-- Vss o-- Gnd o-- Phi_1 o-- Phi_2 o-- Vgg o-- IS o-- IA o-- Sync o-- WS o-- Init o-- Carry o-- Data


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