FLEXIBLE OMNIBUS SYSTEM

A data processing system includes a plurality of units which are coupled to transfer requests including data, command and integrity signals between units over a system bus during allocated bus transfer cycles. Each unit includes response apparatus for acknowledging requests received from other units. Each of a number of units further includes retry apparatus and checking apparatus for verifying that all of the parts of a request received from such unit over the bus are valid. When less than all of the parts of the request are detected as valid, the receiving unit does not accept the request and inhibits its response apparatus from generating a response. This prevents damage to system integrity and permits each unit with retry apparatus to retry the request during a subsequent bus transfer cycle.