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 (1.2 µseconds on the KDF11-U). Depending on the operand modes used in a particular instruction, and the main memory speed (with the asynchronous QBUS), that could add up to roughly 8.5 µseconds (4.2 µseconds on the KDF11-U) to that basic time. (The extra time is roughly linear in the number of memory cycles, at roughly 1.2 µseconds (0.8 µseconds on the KDF11-U) 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
• KDJ11 CPUs

Further reading

• LSI-11/23 Instruction Timing, MicroNote #048
• LSI-11/23 Processor Differences, MicroNote #078
• System Differences - LSI-11 vs. LSI-11/23, MicroNote #049