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The 5 General Interface Management Lines are;
REN
Remote Enable
This is used only by the System Controller to enable devices to be
subsequently placed in the remote progr amming mode. When true, all listeners
capable of remote operation are placed in remote when addressed to listen.
When false, all devices return to local operation. All devices capable of both
remote and local operation must monitor REN at all times. Devices must
respond to REN within 100uS.
The REN command is the only command that will put the instrument into
remote mode. The front-panel keys are disabled, and the ‘Rem’ legend appears
on the display. The ‘Lstn’ and ‘Talk’ legends indicate when the instrument is
addressed.
The instrument may be returned to local operation by sending the GTL
command while the instrument is addressed to listen.
IFC
Interface Clear
This is used only by the System Controller to halt current operations
(communications) on the bus (i.e. unaddress all talkers and listeners and
disable Serial Poll - the idle state). All devices must monitor IFC at all times
and respond within 100uS (minimum pulse width for IFC).
EOI
End Or Identify
When ATN is true the EOI line is used by a controller to execute a parallel poll.
When ATN is false, the EOI line is used by an active talker to indicate the last
byte of a data message.
SRQ
Service Request
This is used by one or more devices to indicate the need for attention and can
act as an interruption of the current sequence of events. Typically SRQ
indicates data is ready to transmit and/or an error condition (e.g. syntax error,
overload, trigger too fast etc.) exists. The controller can mask the SRQ
interrupt and must perform a Serial Po ll of devices (when there is more than
one) to determine who requested service and why.
ATN
Attention
All devices must monitor ATN at all times and respond to it within 200nS. When
true ATN places the interface in the Command Mode where all devices accept
(handshake) data on the DIO lines and interpret it as it Commands (see Multi-
wire Interface Messages below). When fa lse ATN places the interface in the
Data Mode where the active talker sources device dependent Data to all active
listeners. Addresses are sent over the bus during the Command Mode.
3.5 Multiwire Interface Messages (ATN True)
Data transferred on the DIO lines while the controller asserts the ATN line (low) are
bus management commands and device addressing information. This is known as
Command Mode.
GTL
Go To Local
This causes the addressed listener to re turn to local panel control (exit the
REMOTE state). The device will return to remote when REN is sent again.
SDC
Selective Device Clear
This causes the addressed listener to reset to a device-dependent state. This
is the same as DCL (Device Clear) but only affects the addressed device.
PPC
Parallel Poll Configure
Parallel Poll is not implemented. This command is ignored.
