Woodstock HP-21 HP-25

Posted on Feb 7, 2014

The machine used a 12 digit display (8 LED anodes scanned by an Anode driver, and 12 `digits` scanned by a Cathode driver, the latter being used also to scan the keyboard`s 7 columns. The bus is also simplified : 4 lines : the clock`s 2 phases, the Sync line and a new line names Isa multiplexing addresses and data on the system time word.

Woodstock HP-21 HP-25
Click here to download the full size of the above Circuit.

The Power on logic is also included in the ACT and only a few analog elements (4 resistors - only 2 are shown on the HP sketch, 2 capacitors, 1 inductor) are needed along with the 5 chips : ACT (PMOS), ROM1 (PMOS), RAM (PMOS) ROM0 and Anode driver (PMOS) and Cathode driver (bipolar). Note that there is -this time- no big help like the US Patent 4, 001, 5692, for the HP-45 (with an object and source ROM listing, keyed in by Eric Smith in 1995). There are 2 patents related to the HP-25, one is #3, 987, 290, 0ct 19, 1976, granted to Peter D. Dickinson for a "Calculator apparatus for displaying data in engineering notation", the other is #4, 177, 520 for a `Calculator apparatus having a single-step key for displaying and executing program steps and displaying the result`, granted to Randall B. Neff. Two previous study were priceless. Tom NAPIER described back in 1978 the machine time word of the HP-67 (the Woodstock Masterpiece) and commented part of the ROM, and Eric SMITH wrote `NonPareil` a ROM image emulator for the Classic and Woodstock. The HP 25 and Woodstock instruction set is not completely new. In fact, it is an extension of the HP-35`s set. It is now completly deciphered and I wrote emulator of the HP-67 is running faithfully the ROM image code (with the operations of the card reader). But sometimes big differences appear driven by the fast pace of technology evolution. As a result of the integration level progress,...

Leave Comment

characters left:

New Circuits



Popular Circuits

VHF Portable "rubber duck" antenna
Organ Sound Generator
Wien bridge oscillator
Resistor change
Resonance generators by 4011 CMOS Gate
circuit transistor tester
Shock alarm circuit
8051 ps2 lab kit article
Three astable circuit diagram
HD a 3A limit energy-saving three-phase power protection circuit