National Instruments GPIB-SCSI-A, Руководство пользователя

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Appendix E Parallel Polling
© National Instruments Corp. E-3 GPIB-SCSI-A User Manual
Table E-1 contains a list of the parallel poll message bits and a description
of each bit.
Table E-1. Parallel Poll Message Bits
Bit Description
U If 0 (hex 6X), parallel poll is enabled. If 1 (hex 7X), parallel poll
is disabled.
S If the ist (individual status) bit of the device matches the S bit, the
device will set the appropriate data line. Hex 60 through hex 67,
set S to 0; hex 68 through hex 6F, set S to 1.
DIO The value n in bits 0 through 2 corresponds to one of the DIO
lines 1 through 8, where n corresponds to DIO line n+1. Thus, a
value of 2 (binary 010) corresponds to DIO line 3.
Because the U bit is set in all of the PPD messages, they all have the same
effect. All of the PPD messages disable the device from responding to
parallel polls.
Issuing Remote Configurations in S Mode
In S Mode, the ppc function can be used to remotely configure devices for
parallel polls. Remote configuration is indicated by setting the Me bit in the
Command Descriptor Block to 0. For example, if you want to configure a
device at address 5 to respond on DIO line 3 when its ist bit is 1, the
Command Descriptor Block should have a 5 for the device address. The
Me bit should be set to 0, indicating that you want to remotely configure
another device. Additionally, the GPIB-SCSI-A also expects the parallel
poll message byte to be in the Command Descriptor Block. This message is
formed as described below:
U S DIO lines
1 through 8
0 1 1 0 1 0 1 0