KDF11 CPUs

The KDF11 CPUs are single-board PDP-11 CPUs which all use the 'Fonz' F-11 chip set:

• KDF11-A CPU - M8186 - QBUS dual-width CPU used in the PDP-11/23
• KDF11-B CPU - M8189 - QBUS quad-width CPU used in the PDP-11/23+
• KDF11-U CPU - M7133 - UNIBUS hex-width CPU used in the PDP-11/24

The basic clock µcycle is 300 nsec; simple register-register instructions (e.g. MOV, ADD, etc) took 1.7 µseconds. Depending on the operand modes used in a particular instruction, and the main memory speed (with the asynchronous QBUS), that could add roughly 8.5 µseconds to that basic time. (The extra time is roughly linear in the number of memory cycles, at 1.2 µseconds per cycle - PDP-11 instructions could add up to 6 additional memory cycles per instruction, above the 1 needed to fetch the basic instruction.)

Like the LSI-11 models, as a cost-reduction measure they do not have a front panel to control them; instead, when the CPU is halted, specialized microcode used the main asynchronous serial line as a operating console. The command set is named Octal Debugging Technique (ODT); there are commands to read and write main memory, start the CPU, etc.

The main asynchronous serial interface is normally configured so that when the CPU is running, sending a break on the console serial line halts the CPU.

Floating point

All the KDF11 CPUs have two choices for floating point support (full PDP-11 FP11 floating point): a on-board single chip, the KEF11-A floating point chip, which implements floating point using microcode; and a higher-performance co-processor on a separate quad board, the FPF11 (M8188).

The FPF11 communicates with the KDF11 via a flat cable that plugs into the chip socket on the KDF11 where the KEF11-A is installed; is unusual that it can plug into either a QBUS or UNIBUS backplane, since it draws only power from the backplane - all signals come over the cable to the KDF11.

See also

• LSI-11 CPUs