P82 – 40 years revival (b) |

(9) P82 back to life . . . memory and instruction set.

Index — P82 series: archive post — P82 control — revival(a) — revival(b) — revival(c)

MEMORY

No core memory as was in the AGC, same capacity using a single chip CMOS static RAM — yet a distinct downgrade as content is lost when power goes down.

Originally this 16384-bit (2048x8bits) memory was loaded using the HP9825 or short sequences from the keyboard. We are as yet unsure to what extent the 9825 is operational so our tests for now are keyboard initiated. The design defined memory access by 8 pages of 16 blocks by 16 locations. There are some quirks for manual operation in that the displayed addresses are in octal while the keyboard input is in hexadecimal – this took some time to sort out via experimentation and our logic diagrams which are fortunately very good!

top location displayed in octal (selection green keys 8/0/9 — page = 7, block = F, location = F)

A series of memory maps to aid and verify manual entries — plus we can validate all addresses easily via the display & keyboard, just as in the Apollo Guidance Computer “DSKY”!

INSTRUCTION SET

P82 has 55 assigned instruction codes, out of a total of 61:

A. 48 two-key (single byte) instruction codes defined, 5 not implemented – so 43 active.

B. 11 codes defined as operation/operand – 5 are implemented.

C. 2 “verb/noun” codes which invoke an additional cycle for operation with 16-bit word operands. One is DX for storing a full byte instruction into a designated memory location, the second is FX which initiates a 16-bit transfer to a remote smart controller which can interrupt the P82 and return 16-bits of data/status in return.

As well as instructions which can be executed manually or stored in memory, there are the transfer options to determine what will be written to, or read from, an audio device and in which format.

Index — P82 series: archive post — P82 control — revival(a) — revival(b) — revival(c)