Remote Operation
IEEE-488 Interface Overview 5
5-25
Table 5-3. RS-232 Emulation of IEEE-488 Messages
IEEE-488 Message RS-232 Equivalent
GTL LOCAL command
GTR REMOTE command
LLO LOCKOUT command
SDC, DCL ^C (<Cntl> C) character [clear the device]
GET ^T (<Cntl> T) character [execute a group trigger]
SPE, SPD ^P (<Cntl> P) character [print the serial poll string]
UNL, UNT (not emulated on RS-232)
The IEEE-488 interface comes from the IEEE Standards 488.1 and 488.2. For more
information, refer to the standards IEEE-488.1 and IEEE-488.2.
IEEE-488.1 IEEE-488.1 is the hardware piece 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 are for the timing for data interchange. The bus
management lines control the operation of data interchange. The ATN line shows the
operation of the DIO lines for addresses or messages (true), or for DIO data (false). The
EOI line is used with the data lines to show the end of a message, and with the ATN line
for polling. The SRQ line is used by the devices to show the controller that servicing is
necessary. 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
conditions.
IEEE-488.2 IEEE-488.2 is the software piece of the interface, specifying data formats,
common commands, message interchange protocol and the status register
implementation.
Use the subsequent items 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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