National Instruments GPIB-SCSI-A, Руководство пользователя

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Chapter 6 Programming in G Mode
© National Instruments Corp. 6-9 GPIB-SCSI-A User Manual
GPIB Read and Write Termination (END and
EOS)
The IEEE 488 specification defines two methods GPIB Talkers and
Listeners can use to identify the last byte of data messages—END and EOS.
The two methods permit a Talker to send data messages of any length
without the Listener(s) knowing in advance the number of bytes in the
transmission.
END message The Talker asserts the End Or Identify (EOI*) signal
while the last data byte is transmitted. The Listener stops
reading when it detects a data message accompanied by
EOI*, regardless of the value of the byte.
EOS character The Talker sends an End Of String (EOS) character at the
end of its data string. The Listener stops receiving data
when it detects the EOS character. Either a 7-bit ASCII
character or a full 8-bit binary byte can be used.
You can use the two methods individually or in combination. It is
important that the Listener be configured to detect the end of a transmission.
When the GPIB-SCSI-A receives the Command and Status Channel talk or
listen address, no EOS modes are in effect. When talking, the
GPIB-SCSI-A asserts EOI* with the last byte of its response.
When the GPIB-SCSI-A receives the Data Channel talk address, the
GPIB-SCSI-A automatically asserts EOI* on the last byte of data to be
transferred from the SCSI to the GPIB. When the GPIB-SCSI-A receives
the Data Channel listen address, the GPIB-SCSI-A responds to receiving
the END signal from the Talker by stopping the transmission of data
received from the GPIB to the SCSI and starting the sending of a pad byte
to fill the requested count of data transfer. The choice of pad byte is user-
configurable through the
pad
command.