User`s manual

68 PCL-848AB User's Manual
9.4. Bus Commands
In COMMAND mode, bus commands can be placed on the bus and sent to all
devices. These commands have the same meaning regardless of the kind of device.
Each device is designed to respond to those commands that have a useful meaning to
the device and will ignore all others. The operating manual of each device will state
those commands it can recognize.
Bus Command Table
Type Mnemo ASC Bex Purpose
------- --------- ------ ----- --------------------------------------------------------
Universal LLO DC1 11 Local Lockout. Disable front panel local key of
the devices.
Universal DCL DC4 14 Device Clear. All devices are set to a known
state.
Universal PPU NAK 15 Parallel Poll Unconfigure.
Universal SPE CAN 18 Serial Poll Enable.
Universal SPD EM 19 Serial Poll Disable.
Address SDC EOT 04 Selective Device Clear. Clear the listeners to a
known state.
Address GTL SOE 01 Go To Local. Set all listeners into local mode.
Address GET BS 08 Group Execute Trigger. Trigger all listeners on
the bus.
Address PPC ENQ 05 Parallel Poll Configure. Configure a device to
respond to parallel poll.
Address TCT ET 09 Take Control. Transfer control to another
device.
Unaddress UNL ? 3F Unlisten. Unaddress the current listeners.
Unaddress UNT _ SF Untalk. Unaddress the current talker.
9.5. Servioe Request and Serial Polling
Some IEEE-488 devices have the ability to request service from the controller. A
device may request service when it has completed a measurement, or when it has
detected a critical condition, or for other reasons. An IEEE-488 device requests
controller service by setting the SRQ line low. The controller has to determine when
and how a service request will be serviced.
The following sequence is used to respond to a service request:
1) The controller checks for the presence of a service request.