Abstract: There is described a circuit which controls or arbitrates access to a memory unit among a plurality of data processing units. The circuit also manages pointers to different sections of the memory upon a simple one byte request. The circuit also protects the code of the data processing units from illegal write entries.

Abstract: There is described a unique apparatus for exchanging commands and data via a dedicated memory which has ports connected to the data and address busses of two different microprocessors. The system operates even though the microprocessors have different word lengths, e.g. a sixteen bit processor and an eight bit processor. The system permits interfacing between the microprocessors with different bit size words and allows each of the microprocessors to treat the exchange memory as part of its own memory space without locking one microprocessor off of a shared bus.

Abstract: There is provided a circuit which automatically selects one or the other of at least two contending processor circuits and selectively grants the selected processor circuit access to an exchange memory in a regulated and prioritized manner.