Measurement Computing Personal488 rev.3.0 For DOS & Windows 3.Xi - Manual (Page 195)

9I. Operating Modes II. SOFTWARE GUIDES - 9. Driver488/SUB
II-180 Personal488 User’s Manual, Rev. 3.0
System Controller Mode
The most common Driver488 configuration is as the System Controller, controlling several IEEE 488
bus instruments. In this mode, Driver488 can perform all the various IEEE 488 bus protocols
necessary to control and communicate with any IEEE 488 bus devices. As the System Controller in the
Active Controller mode, Driver488 can use all the commands available for the Active Controller state,
plus control the Interface Clear and Remote Enable lines. The allowed bus commands and their actions
are:
Command Action
Abort Pulse Interface Clear.
Local Unassert Remote Enable, or send Go To Local to selected devices.
Remote Assert Remote Enable, optionally setting devices to Remote.
Local Lockout Prevent local (front-panel) control of bus devices.
Clear Clear all or selected devices.
Trigger Trigger selected devices.
Enter Receive data from a bus device.
Output Send data to bus devices.
Pass Control Give up control to another device which becomes the Active Controller.
SPoll Serial Poll a bus device, or check the Service Request state.
PPoll Parallel Poll the bus.
PPoll Config Configure Parallel Poll responses.
PPoll Disable Disable the Parallel Poll response of selected bus devices.
PPoll Unconfig Disable the Parallel Poll response of all bus devices
Send Send low-level bus sequences.
Resume Unassert Attention. Use to allow Peripheral-to-Peripheral transfers.
System Controller, Not Active Controller Mode
After Passing Control to another device, the System Controller is no longer the Active Controller. It
acts as a Peripheral to the new Active Controller, and the allowed bus commands and their actions are
modified accordingly. However, it still maintains control of the Interface Clear and Remote Enable
lines. The available bus commands and their actions are:
Command Action
Abort Pulse Interface Clear.
Local Unassert Remote Enable.
Remote Assert Remote Enable.
Enter Receive data from a bus device as directed by the Active Controller.
Output Send data to bus devices as directed by the Active Controller.
Request Set own Serial Poll request (including Service Request) status.
SPoll Get own Serial Poll request status.
As a bus Peripheral, Driver488 must respond to the commands issued by the Active Controller. The
controller can, for example, address Driver488 to listen in preparation for sending data. There are two
ways to detect our being addressed to listen: through the
Status command, or by detecting an
interrupt with the Arm command.
The Status command can be used to watch for commands from the Active Controller. The Operating
Mode, which is a “P” while Driver488 is a Peripheral, changes to a “C” if the Active Controller passes
control to Driver488. The Addressed State goes from Idle “I” to Listen “L” or Talk “T” if
Driver488 is addressed to listen or to talk, and goes back to Idle “I” when the Active Controller
issues Unlisten ( UNL ), Untalk ( UNT ), or specifies another Talker Address Group ( TAG ). The
Trigger “T1” and Clear “C1” indicators are set when Driver488 is triggered or cleared, and reset
when Status is read. The Address Change indicator is set to Change “G1” when the Addressed State
changes. These indicators allow the program to sense the commands issued to Driver488 by the Active
Controller.
The various Status indicators and their descriptions are provided in the following table: