Remote Operations
IEEE-488 Interface Overview 5
5-23
IEEE-488.1 IEEE-488.1 is the hardware portion of the interface. The parallel signal
lines are divided into eight lines for the data bus, three lines for the handshake, and five
lines for bus management. The handshake lines take care of the timing for data exchange.
The bus management lines control the operation of data exchange. The ATN line
indicates the use of the DIO lines for addresses or messages (true), or for DIO data
(false). The EOI line is used with the data lines to mark the end of a message, and with
the ATN line for polling. The SRQ line is used by the devices to indicate to the controller
that they require service. The IFC line is used by the controller to quickly get all the
devices on the bus to stop talking and start listening. The REN line is used to implement
the remote/local states.
IEEE-488.2 IEEE-488.2 is the software portion of the interface, specifying data formats,
common commands, message exchange protocol and the status register implementation.
Use the following to decode the columns in Figure 5-7. Appendix C shows a typical
IEEE-488 connector and pin assignments.
Type M - Multiline
U - Uniline
Class AC - Addressed Command DD - Device Dependent
AD - Address (Talk or listen) HS - Handshake
UC - Universal Command SE - Secondary
ST - Status
Other B1, B2, etc. - Information Bits Logic Zero = 0 = False
Blanks - Doesn’t Care condition Logic One = 1 = True
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