Abstract: A logic circuit mechanism for inducing a processing unit to release a LOCK signal that the processing unit uses to secure continuous access to a memory system during read modify write operations requiring "atomic" (continuous) access. The processing unit has an internal cache enabling it to set up consecutive memory access operations at a pace such that the LOCK signal could be held continuously active while a string of atomic memory accesses is carried out. The present circuit mechanism prevents premature release of the processing unit's LOCK signal, by asserting a Hold signal which requires the processing unit to release its LOCK signal but only after that unit has fully completed its current atomic access operation.

Abstract: A dual bus microcomputer system including a cache subsystem improves performance under certain circumstances by allowing programmable control over the LOCK function. More particularly, additional logic is coupled between the LOCK output of the CPU and the LOCK input of the cache controller. A control bit from an I/O port is a second input to the additional logic. With the control bit in one state, the logic allows the LOCK input to follow the LOCK output. In the other state of the control bit, the LOCK input is disabled regardless of the state of the LOCK output.

Abstract: A multi-bus microcomputer system includes a cache subsystem and an arbitration supervisor. A CPU is provided with a PREEMPT signal source which generates a preempt signal in CPU cycles extending beyond a specified duration. The preempt signal is effective at any device having access to the bus to initiate an orderly termination of the bus usage. When that device signals its termination of bus usage, the arbitration supervisor changes the state of an ARB/GRANT conductor, which had been in the grant phase, to the arbitration phase. During the arbitration phase each of the devices (other than the CPU) cooperates in an arbitration mechanism for bus usage during the next grant phase. On the other hand, the CPU, having asserted preempt, responds to a signal indicating initiation of the arbitration phase by immediately accessing the system bus.

Abstract: A network arbitration period following the termination of each transmitted frame is divided into a plurality of access windows which are assigned to respective stations in the network. Any station desiring to gain access to the network can acquire the network by transmitting during its assigned access window if no station assigned an earlier access window has already begun transmitting. The access window assignments can be rotated to equitably distribute access to the network.