Input Buffer Operation - Fluke 5500A Operator's Manual

Remote Operation
5
Remote Program Examples

5-66. Input Buffer Operation

As the 5500A Calibrator receives each data byte from the controller, it places the bytes
in a portion of memory called the input buffer. The input buffer holds up to 350 data
bytes and operates in a first in, first out fashion.
IEEE-488 The 5500A Calibrator treats the EOI IEEE-488 control line as a separate data
byte and inserts it into the input buffer if it is encountered as part of a message
terminator. Input buffer operation is transparent to the program running on the
controller. If the controller sends commands faster than the calibrator can process them,
the input buffer fills to capacity. When the input buffer is full, the calibrator holds off the
IEEE-488 bus with the NRFD (Not Ready For Data) handshake line. When the calibrator
has processed a data byte from the full input buffer, it then completes the handshake,
allowing the controller to send another data byte. The calibrator clears the input buffer
on power-up and on receiving the DCL (Device Clear) or SDC (Selected Device Clear)
messages from the controller.
RS-232 Under RS-232-C serial port remote control using ^S (<Cntl> S) XOFF protocol,
the calibrator issues a ^S XOFF when the input buffer becomes 80% full. The calibrator
issues a ^Q (<Cntl> Q) when it has read enough of the input buffer so that it is less than
40% full. When using RTS (Request to Send) protocol (selected as part of the "RS-232
Host Port Setup Procedure"), the serial interface asserts and unasserts RTS in response to
same conditions as for XON/XOFF protocol.
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