Measurement Computing Digital232 - Manual (Page 40)

Section 3 Command Descriptions
3.18
Data Ready Rn
The Data Ready command enables digital input data to be latched and
transmitted out the serial port. When used in conjunction with the Service Request
function, the External Data Ready line can both latch the input data and signal the
host computer that new data is available.
In the default mode (R0) data is read and transmitted out the serial port when the
Digital232 receives an R0 command. In R1 mode, data on an input port is latched on
the transition of a signal applied to the External Data Ready (EDR) line. At that
same time, the latched data is transmitted out the Digital232’s serial port to the host
computer. If EDR transitions again before the previous EDR buffered data has been
formatted for output and sent to an internal serial output queue, the Digital232 will
generate an EDR Overrun error and ignore the EDR read request.
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).
In the R2 mode, serial data is sent to the host every time the last serial terminator
is received. If, for example, the serial terminators selected are CR and LF then data is
read and transmitted on receipt of the LF.
R0 Data is read and transmitted to the serial host computer.
R1 Data is latched on an EDR transition and transmitted to the host.
R2 Data is sent to the host computer after every receipt of the last serial
terminator from the host
Example:
@ reset the Digital232
R1 request digital I/O data to be sent to the serial host