Measurement Computing Digital488 - Manual (Page 38)

Section 3 Command Descriptions
3.8
Data Ready Rn
The Data Ready command enables digital input data to be latched. When used in
conjunction with the Service Request (M2) command, the External Data Ready line
can both latch the input data and signal the controller that new data is available.
In the default mode (R0) data is read when the Digital488 is addressed to talk. In
the R1 mode, it will wait for the selected External Data Ready (EDR) transition before
reading the data and formatting it for output. If the Digital488 is addressed to talk before
EDR is asserted, the bus will hang up until the EDR pulse occurs. Once EDR is asserted
the data will remain latched until the interface is addressed to talk and the data is read by
the controller. If EDR transitions again before the previous EDR buffered data has been
output, the Digital488 will generate an EDR Overrun error and ignore the EDR read
request.
After output in the F0 through F4 formats, the Digital488 must be re-addressed to
talk to perform subsequent buffered output of EDR captured data. EDR cannot be used
to capture data in the F5 high speed binary format
The EDR signal must be at least 1 microsecond wide and should have a rise and
fall time of less than 1.0 microsecond. The EDR line defaults to rising-edge sensitive, but
can be changed to falling-edge sensitive with the Invert command (I32).
R0 Data is not latched, and is read whenever the Digital488
is addressed to talk
R1 Data is latched on an EDR transition
Example:
CLEAR 718 reset the Digital488
OUTPUT 718;"R1X" data is only read after a rising-edge
signal is applied to the EDR line