Method and system for expanding the i/o on i/o limited devices

Abstract

An I/O system includes a Digital Device selecting a digital output to be set and a Digital I/O Expansion Mechanism, electrically coupled to the Digital Device. The Digital I/O Expansion Mechanism includes an input bank, a FIFO, and an I/O line. The Digital I/O Expansion Mechanism clears a stored value in the first input bank, samples the first value of the first input bank, and detects a change in the input bank. The Digital I/O Expansion Mechanism also stores a state of a data bit of the input bank along with a bank identifier in the FIFO. The Digital I/O Expansion Mechanism still further samples the I/O line via a first READ cycle and drives the I/O line with a next data entry from the FIFO. Digital I/O Expansion Mechanism samples all digital inputs and stores any detected changes in the FIFO. The Digital I/O Expansion Mechanism transmits all values in the FIFO to the Digital Device during a subsequent READ cycle and transmits to the Digital Device a last value read. The Digital I/O Expansion Mechanism also changes a digital output when a first WRITE command occurs and the Digital Device explicitly selects the digital output to be set and writes an entire bank in response to a bit change. Additionally, the Digital I/O Expansion Mechanism decodes and latches the digital output until the digital output is overwritten via a second WRITE command to the input bank from the Digital Device.