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3.4.1.1 Polling Commands
The IEEE standard provides two methods of determining the status of the devices in the system;
namely serial poll and parallel poll. The parallel poll produces up to 8 bits of status from up to 8 dif-
ferent units simultaneously. A parallel poll is very fast but provides limited information. The serial
poll provides 7 bits of status from one unit at a time.
3.4.1.2 Parallel Polling
The model 3940/3944 provides for software configuring of which bit and with which polarity the unit
should respond. This bit is “true” when an error condition exists. (“ERR” displayed on the panel). Con-
figuring needs to be done only once or anytime the software desires to change the configuration. The com-
mands related to parallel poll are as follows:
For sample sequences, see section 6.5.4 of the IEEE-488 standard.
IEEE-488
Command
Mneonic
Result
Configure
PPC
Places unit into a state where it expects par-
allel poll enable and disable commands to
establish which bits should be set or selected
in response to a parallel poll.
Unconfigure
PPU
Removes unit from PPC state (UNL does the
same, but also unlistens device).
Enable
PPE
When unit is in PPC state, it indicates which
bit and which polarity the device should re-
spond. Hex codes 60-67 selects bits 0-7 re-
spectively to be set to 0 for a true error re-
sponse. Since logic 0 is HI on open collector
lines, this provides a logical “OR” of al units
designated to respond with a given line. Hex
codes 68-6F selects bits 0-7 respectively to
be set to 1 for a true (error) response. This
can provide logical NAND of all units desig-
nated to respond, with a given line.
wrap
default Disable
PPD
Clears any configuration previously entered.
This is valid only when unit is in PPC state.
Section 3 - GPIB Programming
3-7
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