View source for FPF11 floating point processor

The '''FPF11 floating point processor''' is an optional [[co-processor]] module which provides high-performance [[floating point]] for [[KDF11 CPUs]] (which use the [[F-11 chip set]]); it implements [[FP11 floating point|FP11]]-compatible [[floating point]].

It is a [[DEC card form factor|quad]] [[printed circuit board|board]] (the M8188) which plugs into the [[backplane]] slot next to the [[Central Processing Unit|CPU]] board. It only gets power from the backplane, though; a [[flat cable]] connects the FPF11 to the CPU board; it plugs into the [[chip socket]] which the [[KEF11-A floating point chip]] normally goes into.

That socket gives the FPF11 access to both the [[data bus]] and the [[microinstruction]] [[bus]] on the CPU card. The FPF11 contains [[microcode]] to control both the main CPU, and the  [[hardware]] on the FPF11. The main CPU is sent [[no-op]] microinstructions when there is nothing for it to do; e.g. when the FPF11 does not need it to [[fetch]] data from, or [[store]] it in, [[main memory]].

Control of the main CPU is transferred to the FPF11 in the same way as to the KEF11-A when a floating point instruction is seen; but while the latter uses the hardware on the CPU to perform all its calcuations, the FPF11 has extensive hardware to perform floating point calculations at higher performance, on-board.

The FPF11 has its own [[clock]], which is not synchronized to that of the main CPU; the FPF11 can re-synchronize with the main CPU when control is to be transferred back to it, when the floating point instruction is completed. It also supports clocking for [[microcycle]]s of shorter duration, which its microcode can select, as needed, to run individual microcycles as fast as possible.

The floating point [[register]]s are actually on the FPF11 (probably for performance), unlike those for the KEF11-A, which are in the [[KTF11-A memory management chip]].

[[Category: PDP-11 Processors]]