Abstract: An Input/Output Module (IOM) interfacing multiple computers attached to a dual system bus. The IOM provides an interbus module which interfaces the dual system bus to a sub-requestor bus connecting multiple sub-requestor modules. The sub-requestor modules control a plurality of interface adaptors permitting data transfers to/from a variety of peripherals using different data protocols and clock rates. The requirements for the main host processors and memories in a computer system would be unduly burdensome were it not for the relief from these overhead operations by the input/output module which provides the tailoring of data transfer capability to and from a multiplicity of peripherals having many different types of protocols and clock rates.

Abstract: An apparatus is disclosed that provides control of access to a module. In particular, the module should not be accessed while in a busy or unstable state. The module disclosed herein, by way of example, is a timer module. Access to the timer is controlled by the disclosed apparatus while the timer is changing state.

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.

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.