Looking for parts for an HP 9821A desktop calculator

Wow! The 9821 is, I beleive, by far the rarest of that family... Yes, or rather I can confirm that the 9810 and 9830 use the same CPU cards. I have both machines, and I've interchanged CPU cards between them (in both directions) with no problems. The CPU cards have the same part numbers too... In case you've not figured it out yet, the part numbers of the cards in these machines start with the model number of the machine where they were first used (and the 9810, using 09810-665xx cards, came out first). You may also find 09865-665xx cards in the cassette drive controller -- you do in the 9830, for example. The card handles of the cards give the last 2 digits of the part number, using the obvious code (if you can't work out what the 'obvious code' is, then you shouldn't be inside the machine in the first place ;-)). The CPU boards are : 09810-66511 (Br/Br) I/O interface 09810-66512 (Br/R) CPU Clock and I/O logic 09810-66513 (Br/Or) CPU control (microcode, etc) 09810-66514 (Br/Y) CPU data path Here are some notes about the 98x0 CPU that were sitting about on this PC. I've got some more info like this on the 9810 and 9830 machines (discovered by pulling them apart carefully :-)) if anyone is interested... --------------------------- There are 4 PCBs, each with about 20 chips. Mostly TTL (including 74Hxxx numbers -- watch out, these can have odd pinouts). 9 small (256*4) PROMs (Microcode and ALU lookup tables). The boards (like all those in the machine) have colour-coded handles which relate to the last 2 digits of the part number (the rest of the number is always 09810-665xx) using the obvious code. Here's roughly what goes on on the CPU boards (Br handle on rear): Data path (Br/Y). ALU (2 PROMs as a lookup table) -- 1 bit for binary operations, 1 nybble for BCD ('decimal'). 2 flags (in 7474) for carry and decimal carry. Main registers : A Accumlator is 16 bits with nybble access to the ends ('95 -> '91 ->'95). B and P registers are 16 bit, serial only (9328s). E register is 4 bits, serial only, used to store one nybble during shifts? Includes one of the bit muxes for the ALU input ('53 with '62 expander). The other one is on the memory data PCB (!). Note that memory can be read by nybble too (the low 4 bits of the T register (memory data register) are brought to this PCB. Therefore BCD operations are A=A+memory kind of things. Control (Br/O). Microcode PROMs obviously (but they're not all next to each other, so watch out!). Also microcode program counter (4 off 'H108 JKs). Note that the next microcode address field specifies the bits to _change_ (it's connected to the J and K inputs on the FFs), which is odd. One half of this field also selects the branch condition, which affects one bit in the other half (writing this microcode must have involved some serious hackery!). 16 input condition mux (from carry flags, I/O flags, LSB of P register, and many bits of Q). Also Q register (16 bit SR, used to store instruction fetched from memory. Microcode field decoders ('155s, used as 3-8 decoders) A/B register select FF ('H101). Test connector on top of PCB carries microcode address, microcode address changes, condition mux output, so you can see what the machine is doing (given a logic analyser and a microcode listing!). Clock (Br/R). Master clock obviously. Note the pads to connect an external TTL clock generator to -- shorting the 2 on the solder side together disables the internal osciallator. These signals are also on (unconnected) fingers on the edge connector. Also the /n counter to produce the microcode clock (this thing will generate 1-16 shift pulses for each instruction -- set by a field in the microcode word -- so it can do n-bit operations between the main registers) + control logic. I/O function register (loaded from Q) and decoder (The '154 in the middle of the board). I/O clock is odd. It's generated via that decoder by fiddling with the instruction in the I/O command register (done via some of the gates), which means it runs at half the main clock speed. So does the bit clock during I/O operations (!). Thrre's a FF on the I/O card to synchronise this. I/O operation FF (the 'H101). Other random logic for I/O control. I/O bit counter. I/O (Br/Br). I/O data register (16 bit, parallel and serial access) + control logic. Note that for external devices, that's 8 bit data, 4 bit select (address), 4 bit control. For internal devices (keyboard, display, card reader, printer), it's 16 bit data, selects come from other logic). Also sync FF at the input to this, control gating. Several SR FFs (made select and control. Memory cage (R handle at rear) ---- NOTE THIS IS 9810 SPECIFIC!!. R/Pu is the backplane, and contains no other electronics. There's a test connector on top (36 pin) which gives +5V, ground, the 16 bits of M (address) and 16 bits of T (data), but with no sync signals). At the bottom, the rear connector carries power and CPU signals (mostly bit-serial). The front connector is parallel address, data, selects for the cartridge ROMs, and is routed to the cartridge backplane only. ROM (R/Br) system firmware. Note that HP ROMs are strange, needing a -2V or so bias supply and both normal and inverted forms of the highest address bit. The selects (CE And CS) need to be taken to +12V to enable the ROM (this is done on the address PCB for all ROMs, including those in cartridges). TIming/Control (R/R). Memory cycle timing (counter, '154 decoder, gates). Refresh counter and mux for DRAMs. Refresh timing monostable. Low 5 RAM address buffers (address bits from refresh mux, you see). Drivers for R/W and Precharge lines to RAM. M and T register control gates Address (R/Or). M (address) shift register (16 bit). Address decoder (note that ROM and RAM are in the same address space, and neither are contiguous!). RAM address buffers, ROM and RAM CS buffers. ROM address gates Data (R/Y). T (data) shift register, bit doubling logic for RAM read (the RAM is only half width, so 2 cycles are done with a shift between them for reads -- this is handled by the control/timing PCB, not the CPU). RAM data buffers (read and write). RAM (R/Gn, R/Bu). 1103 DRAM chips (1K *1 bit, PMOS, odd voltage levels). Nothing more. RAM is either 8 bit (data store, doubled to 16 bits on the data PCB)< or 3 bit (program store, doubled to 6 bit (keycodes)). RAMs are labelled in the etch with their bit number which helps. ------------------------------------- I cna tell you that the 9810 and 9830 have very different memory cards. The 9810 has a little memory cage with its own backplane containing cars about the same size as the CPU cards (see the descriptions above). The 9830 has larger cards that go across the whole width of the machine -- up to 2 RAM cards (4K 16 bit words each max, in 1103s), 1 main ROM card (28 ROM chips !), Memory control/address, Memory Data, Extension ROM Selector, a card with 2 more ROM chips that wouldn't fit on the main ROM card (!), and up to 3 intenral extension ROM cards.... If you need help with repairing any of the cards that are also used in the 9810 or 9830 (check the part numbers), just ask. I have worked on these machines at the component level... I do not have any spare cards, though. -tony