FPP-12 Floating Point Processor

This manual details the Digital Equipment Corporation's Floating Point Processor (FPP12), a peripheral device designed for PDP-8 and PDP-12 computers, covering its programming, hardware, and installation.

The FPP12 is a programmable, parallel digital processor that connects to the CPU's I/O bus and uses direct memory access (DMA) to "steal" memory cycles, significantly accelerating floating-point arithmetic (20-100 times faster than software). It supports both parallel operation with the CPU (sharing memory cycles) and a faster serial mode (locking out the CPU). The document describes its floating-point and fixed-point number systems, which use a 12-bit signed exponent and a 24-bit signed mantissa, with calculations performed at 28-bit precision before rounding to 24 bits.

Key programming aspects include the FPP12's eight registers (like the Floating Point Accumulator, Program Counter, and Index Registers) and the Active Parameter Table (APT), which stores information for program initialization, restarting, and debugging. The instruction set features data reference operations (load, store, arithmetic) and special instructions for index register manipulation, conditional jumps, and pointer moves, supporting 24-bit absolute or 12-bit relative addressing. Initialization and status interrogation are managed via PDP-8 IOT instructions, with specific instructions like FPHLT allowing program abortion or single-stepping for debugging.

Hardware descriptions detail the FPP12's components, including new MSI modules, and its organization into six major operational states: INITIATE, FETCH, PROCESS, EXECUTE, DEPOSIT, and EXIT. The manual provides flow diagrams for each state and instruction type, explaining the internal logic, data flow, and data break control mechanism.

Installation guidelines cover cabling for various PDP-8/PDP-12 bus configurations, necessary wiring alterations, and module changes for different bus types. It also outlines AC power requirements and lists diagnostic programs for check-out. Dedicated maintenance IOTs allow detailed examination of the FPP12's internal state, aiding in troubleshooting and debugging.