Importance

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Abstract

The destination of commands provided by a microcomputer to an input-output unit over a data bus is provided without an address bus, while a control circuit in the input-output unit is connected with the microcomputer by connections for only three binary signals in one direction, 'clear', chip-select and data strobe and one in the other, namely interrupt. The control circuit has a decoder connected to the data bus that sorts out the commands, feeding the outputs through a gate array that are enabled by the chip-select and data strobe signals for timing. Commands for switching, such as beginning and ending counts, and so on are one-byte commands directly transmitted to the appropriate circuits of the input-output. Read and write commands are two-byte commands sequenced by a sequencing and lockout circuit, the circuit selected in first byte being activated to read or write to or from the data bus in the second byte while the decoder is blocked. The direction of transmission of the data bus is controlled over a single connection from the control circuit in accordance with whether a write command is or is not present.

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First Claim