HP 9810

Very wise. I am thinkign of a quote fdrom the TRS-80 (model 1) Techncial Manual, when DRAMs were expensive. It's something like 'Sometimes replaceing all the RAMs as a set is less constly on your nerves than fighting a losing war with one bit' :-) Gettign back to the 9810. The good news is that the PSU is relatively simple nad quite friendly to work on. The 5V regualtor is a switcher, but oen hat takes in about 16-0-16V AC from a transformer secondary winding. DO a lot nicer to work on than a mains swticher. The bad news is that I would not be surpised if when you've got the supply working you still ahve no dispaly. Logic faults in these machiens re alas common after 40 years or more. The machines is, in a sense, how you'd design a calculator today. It's a gneral-purpose procesosr (albeit with a few specific machine instructions fo the clacualtor) with the keyboard, display, priinter, card reader, etc as peripherals. And running firmware form RO Mthat makes it into a calculator. The processor is , of course nto a signle chip. It's 4 boards of TTL, around 80 ICs. It's a bit serial [1] 16 bit machine with a programming model somewhat like an HP2100 mini, but not exactly the same. The 4 baords contain I/O interface (int's a bit seiral procesos,r this board contaisn a 16 bit shift register ot communicate in pralalle with the peripherals., There are 16 outpus and 12 inputs, When communicating with external deivces, the 16 outputs are 4 addres bits, 4 status biuts, 8 data bits, the 12 inps ade 4 status, 8 data. Clock gnerator and I/O control. There are 2 main procssor clocks. I call them bitclk (which clocks the data shift registers) and muclk (which clocks the microcode program counter). The thing can generate 1-16 bitclks between muclks, controleld by the microcode. Rememebr it's bit serial. This lets it repeat a bit operation 1-16 tims, so that, for example, addign 2 registers cna be done in one microinstruction (with a clock count of 16 bitclks). The second part of this PCB contains the I/O control state machine CPU control. This contains the 256*28 bit microcode [2]. microcode sequencer, condtion logic, etc Data path The main registers (but one -- the Q register is on the cotnrol board, and the memory address and data registers are in the memory box), the ALU (which is a pair of ROMS programmed as look-up tables), carry flags, etc. [1] No, thatwould be too simple. It's bit serial for binary operations and nybble-serial for BCD operations. [2] If you want a listing of the PCU microcode, just ask... The memeory box -- the metal box onthe left side of the system -- contains : ROM board. 8 off HP 512byte ROMs. Actually, they're mroe like 2*256*8 bits, the metlisation layer tht definees the ROM contents can either conenct them as 256*16 ,r o(as here) 512*8. A side-effect of this is that there are seprate enables for the 2 halves, conventionally claled A8 and A8/ I bleieve that if both are low at hthe smae time you get the lgocial AND of the 2 bytes... RAM board. Itell 1103 1K*1 DRAms. There is one standard board, there may be an expansion DAM board too. The REAM is odd. Foe one thing the memory cotnrol system does 2 RAM cycles for each operation, the RAM is only half as wide as you'd expect. SO the system/data RAM is 8 chips. User programs are stored as 6 bit keycode,s so they are stored in sets of 3 chips. I cna't think of antoher machine thgat uses 3 bit wide RAM... Memory Address This contaisn the M register (memory addresss), address decodeer, etc Memory Data. The T register (Memory data), data buffers, etc. Memory timing. Tiis produces the cotnrol signals for the ROMs and RAMs, does the double RAM cycle, refreshes the RAM, etc. The dispaly is a peripehral to the processor, It takes the 16 bits fro mteh I/O register and tuses them as : 1 bit not used 3 bits (1-of-n) to select a line of the display (X, Y, Z) 4 bits to select a digit in the line (binary encoded) 8 bits to control the segments of that digit (includignthe decimal point) So fi the processor isn't working, or there's a problem wit hthe ROM or the RAM, there will be no display. Debuggign it is fun, provided you set about it logically. Think of it as a 16 bit bit-serial minicomputer :-). A logic analyser is almost esential in a lot of cases, though. You will also have a couple of mechancial repairs to do (not 'may', 'will). The card readerrolewlrand printer platen will have decayed with time. The platen can be fairly easily rebuilt with Cold Shrink. The card reder rolelr is a bit harder. There are 2 methods I've heard of. One is to bit O-rogns over the origianl hub and hope they stay on The other is to make a new hub with grooves for O-rings. It's up to you... -tony