Pump bus to avoid indeterminacy in reading variable bit field

摘要

A data field having a variable number of zero-level bits is read by a bus in a digital system, wherein the bus is pumped by writing all logical "one" bits onto the bus lines just before they are read. The unused bits will then be still in a logical "one" state, i.e. a known value, rather than floating or at an indeterminate value. A program for performing this operation in a computer uses steps to prevent other operations such as refresh cycles or interrupts from being interposed between the write and read cycles. A CPU may use this method to read a system identifier value upon boot-up, for example.