Martel Electronics M2000 - Manual (Page 18)

because if many errors occur before the user can acknowledge and read them, the earliest
errors are the most likely to point to the problem. The later errors are usually repetitions or
consequences of the original problem.
Input Buffer Operation
As the M2000 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 250 data bytes and operates in a
first in, first out fashion.
IEEE-488 The M2000 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 opera-
tion is transparent to the program running on the controller. If the controller sends commands
faster than the M2000 can process them, the input buffer fills to capacity. When the input
buffer is full, the M2000 holds off the IEEE-488 bus with the NRFD (Not Ready For Data)
handshake line. When the M2000 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 ( S) XOFF protocol, the
M2000 issues a ^S XOFF when the input buffer becomes 80% full. The calibrator issues a
^Q ( Q) XON when it has read enough of the input buffer so that it is less than 40%
full.
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