Abstract: The logic circuitry of an IC chip is connected to JTAG register chains which hold state information on each portion of the logic circuitry therein. A JTAG Tracker Module is connected to the controls of each of the JTAG register chains enabling a programmer-operator to read the present state of each JTAG register chain and enabling a readout of the logic circuits condition in a single clock period.

Abstract: A single chip data path gate array interface links a central processing unit, operating at a first clock rate and single word protocol, to dual system busses operating at a second clock rate and multiple-word protocol. The data path interface holds command, data and message registers, controlled by external logic, in an input channel pathway and an output channel pathway. The interface chip is basically limited to registers and multiplexers making it flexible for use in different architectures such as both Store-Through and Non-Store-Through cache protocols. In addition, such a simplified chip is simple to fabricate and to maintain free of defects.

Abstract: A network of digital modules having store-through and non-store-through cache memories, is provided with intercommunication capability by means of two sets of system busses each of which are replicates of each other. The system busses provide a higher throughput by both being available to each of the digital modules so that a requesting digital module can alternately use a second system bus if the first system bus happens to be busy. Failure of one system bus will allocate transmission service to the second operating system bus thus providing redundancy. Alternatively, each of the system busses can be isolated for partitioning the digital modules into two different operating systems which are independent of each other.

Abstract: An error logging system where errors are captured on dual system busses operating at a lower clock rate (16 MHz) than the processor which receives the error information. The system functions to substantially reduce the loads on the processor in addition to maximizing the use of the system bus drivers which are pin-constrained. The processor operates at a higher clock rate (32 MHz). Processor commands to read error data from an error log register are synchronized down to the 16 MHz rate, then enabled onto a processor bus after a second synchronization operation back to the higher (32 MHz) rate. Provision is made for identifying several different types of error categories.

Abstract: A memory module is used in multiples on a bus in a data processing system. Each memory module comprises a plurality of storage cells, an input circuit for receiving a read command and a read address from the bus, and a compare circuit which generates a match signal when the read address is within a selectable address range for the storage cells. Also, the module further includes: a control circuit, coupled to the compare circuit, which responds to the match signal by almost always executing the read command in a small time interval on the bus and occasionally executing the read command in a long time interval. Further, the module includes a bus transmit circuit, coupled to the control circuit, for sending a control signal on the bus if the control circuit selects the long time interval.

Abstract: A User bus lockout prevention mechanism for use in a time-shared bus, multiple bus User, computer architecture where bus Users have private cache systems which perform a cache cycle when a WRITE TO MEMORY instruction occurs on the bus to determine if data cached from main memory has been overwritten in main memory. A User can be locked out from use of the bus if a synchronism occurs between repetitive cache cycles and periodicity of the request Retry mechanism of the User. Bus lockout is prevented by controlling the Retry mechanism of the User to retry requests in accordance with a sequence of varying retry wait intervals. The sequence comprises bursts of short wait intervals interleaved with long wait intervals, the sequence beginning with a burst of short wait intervals. The wait interval durations of the first and second occurring bursts are interleaved with respect to each other. The second occurring long wait is longer than the first occurring long wait. The sequence is terminated upon bus grant.

Abstract: A User bus lockout prevention mechanism for use in a time-shared busy multiple bus User, computer architecture where bus Users include private cache systems which perform a cache cycle when a WRITE TO MEMORY instruction occurs on the bus to determine if data cached from main memory has been overwritten in main memory. A User can be locked out from use of the bus if a synchronism occurs between repetative cache cycles and periodicity of the Retry mechanism of the User. Bus lockout is prevented by the User with the cache issuing an INHIBIT WRITE to the bus when a cache cycle is being performed. Other Users inhibit issuing WRITE TO MEMORY requests to the bus until the INHIBIT WRITE signal terminates. Bus requests other than a write request may be issued to the bus during INHIBIT WRITE.