5502A
Operators Manual
5-50
Input Buffer Operation
As the Calibrator receives each data byte from the controller, it puts the bytes in a part of
memory the input buffer. The input buffer holds a maximum of 350 data bytes and
operates with first in, first out protocol.
IEEE-488 The Calibrator sees the EOI IEEE-488 control line as an isolated data byte
and puts it into the input buffer if it is met as part of a message terminator. Input buffer
operation is transparent to the program 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 completes the handshake, and lets the controller send a
different 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 with ^S (<Cntl> S) XOFF protocol,
the Calibrator gives a ^S XOFF when the input buffer becomes 80 % full. The Calibrator
gives a ^Q (<Cntl> Q) when it has read a sufficient amount of the input buffer so that it is
less than 40 % full. When you use 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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