Measurement Computing Micro 488/EX rev.2.1 - Manual (Page 29)

Section 2 Getting Started
2.15
-RxD Receive Data - Input - Pin 2
This pin accepts serial data sent by the RS-232 or RS-422 host. The
serial data is expected with the word length, baud rate, stop bits and
parity selected by the internal switches. The signal level is low true.
-TxD Transmit Data - Output - Pin 3
This pin transmits serial data to the RS-232 or RS-422 host. The
serial data is sent with the word length, baud rate, stop bits and parity
selected by the internal switches. The signal level is low true.
CTS Clear To Send - Input - Pin 4
The CTS input is used as a hardware handshake line to prevent the
Micro488/EX from transmitting serial data when the RS-232 host is
not ready to accept it. When RTS/CTS handshake is selected on the
internal switches, the Micro488/EX will not transmit data out -TxD
while this line is un-asserted (low). If the RS-232 host is not capable
of driving this line it can be connected to the Vtest output (Pin 6) of
the Micro488/EX. If XON/XOFF handshake is selected, the CTS line
is not tested to determine if it can transmit data.
RTS Request To Send - Output - Pin 5
The RTS output is used as a hardware handshake line to prevent the
RS-232/RS-422 host from transmitting serial data if the Micro488/EX
is not ready to accept it. When RTS/CTS handshake is selected on
the internal switches, the Micro488/EX will drive the RTS output
high when there are greater than 1000 character locations available in
its internal buffer. If the number of available locations drops to less
than 1000, the Micro488/EX will un-assert (low) this output. If
XON/XOFF
handshake is selected, the RTS line will be permanently
driven active high.
Vtest Test Voltage - Output - Pin 6
This pin is connected to +5 volts through a 1K
Ω resistor. It is also
common to Vtest on pin 9.
Gnd Ground - Pin 7
This pin sets the ground reference point for the other RS-232 inputs
and outputs.