What was the Molecular instruction set?
The Molecular word size is 18 bits, and the basic memory is 32K words. The machine was generally known as the Molecular-18 for this reason. The MSB (Bit 18) was a parity bit, so for all intents and purposes it was a 17 bit machine. The minimal CPU contained the following registers: PC – Program counter MA – Memory address REGA – Register A REGB – Register B. C – Carry Flag GT – Greater Than Flag Operation codes 2 through to 26 – Memory reference instructions These instructions operated on either current page or zero page. All of these instructions could operate indirectly. Instruction words are organized as follows: |17|16|15|14|13|12|11|10| 9| 8| 7| 6| 5| 4| 3| 2| 1| | | | | | | | |OP-CODE |I |Z | —– Memory Address —— | I = Indirection Flag Z = Zero Page Flag 02 – JUMP Jump to address 15 – ADAC Add to Reg A with carry 03 – JSBR Jump to subroutine 16 – ADBC Add to Reg B with carry 04 – INSZ Increment and skip on zero 17 – SFAC Subtract from Reg A with carry 05 – DESZ Decrement a
