KDJ11 CPUs

There are several single-board CPUs which all use the 'Jaws' J-11 chipset:

• KDJ11-A CPU - M8192 - QBUS dual-width CPU
• KDJ11-B CPU - M8190 - QBUS quad-width CPU used in the PDP-11/83 and PDP-11/84
• KDJ11-E CPU - M8981 - QBUS quad-width CPU used in the PDP-11/93 and PDP-11/94

Floating point

All the KDJ11 CPUs have two choices for floating point support (full PDP-11 floating point, as in the FP11-B and FP11-C): the base chip implements floating point using microcode; and a higher-performance separate chip, the FPJ11.

ODT

The J-11 chip set includes microcode which provides 'front panel' functionality named 'ODT'; the ability to read and write to memory, start the process, etc. Unlike the ODT in the KDF11 CPUs, which only supported 18-bit addressing, the KDJ11's do not have this limitation.

Note, however, that the KDJ11-A and KDJ11-B power up with the cache enabled, even for ODT, so if the user writes some data into a given location using ODT, and then reads it back, they will get the correct data even if that memory location is faulty - the CPU is getting the (correct) data from the cache.

To have 'memory' reads and writes actually go to the memory, the cache has to be turned off:

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Note that starting the machine does an INIT, which will again enable the cache.