FP11-C Floating-Point Processor

The FP11-C was a FPP used in the PDP-11/45 and PDP-11/70 computers (KB11-D and KB11-C CPU variants thereof, respectively); it operated in parallel with the main processor, so that two instructions (one floating point, one regular) could be processed at the same time.

Like the FP11-B, it supported short (32 bit) and long (64 bit) floating point numbers; both forms used an 8 bit exponent (in 'excess 0200' notation, giving an exponent range of +127. to -128.), a sign bit, and the remaining bits were the fractional part. A state bit controlled whether the FP11-C operated in short or long mode.

The FP11-C contained 6 internal registers, each capable of holding either a short or long floating point value.

Implementation

The FP11-C used a clock which is synchronized to the basic CPU's clock. It plugged into special pre-wired slots in the CPU's backplane, and included the following boards:

• M8128 ROM and ROM Control
• M8129 Exponent and Data Path
• M8126 Fraction Data Path - High Order
• M8127 Fraction Data Path - Low Order