Interface system wherein the interface is addressed before data transfer from a selected device

Abstract

An interface system for expanding the number of device input ports and compatable with the message format and bus structure of a standard interface, namely the IEEE standard 488, has address decoding logic which identifies the expansion system and is operative to select, in accordance with an incoming message on the bus, which of several ports is to transmit or receive messages via the bus. Under control of the port identification message and strobe signals obtained from the handshake control logic of the expansion system, a sequence containing a predetermined number of bytes of port data is transmitted to the bus. The port data bytes may be coded in various formats, desirably BCD, which is compatable with the digital output format of many devices which may be interconnected and interfaced by the expansion system with the bus. Manual control is enabled by the control messages which are received by the expansion system, such that the transmission of messages to the bus from the selected port or from any device connected to the bus may, if desired, be inhibited until the manual control is activated. Different control messages may be used to enable the transmission of different message sequences with or without activation of the manual control.

Dependencies are inferred from the claim text.