The CPB is the CPU for the P856 and P857. It is built around four 74181 bitslices. There is an NS 8576 PLA (used for instruction decoding) and an AY-5-1013A or COM2502 UART for serial communications.

Documentation

See the P856M/P857M documentation on the Docs page.
CPB_DSC_2257_800.jpg
CPB with COM2502 UART
CPB_DSC_2265_800.jpg
CPB with AY-5-1013A UART