Oxford Instruments Mercury iTC, Handbook

Page: 62 / 146

Handbook
November 2011 / 59-UMC0071 / Issue 01
Mercury iTC
Page 62
FUNCTIONAL DESCRIPTION
Original Instructions
4.2.5.1 Serial RS232 interface
The RS232 interface is connected via a 25-way D-socket on the rear panel. The iTC is
configured as Data Circuit-terminating Equipment (DCE), with the standard pin-
assignations listed in
Table 4-3 .
Most computer RS232 interfaces are configured as Data Terminal Equipment (DTE). If
the computer has a 25-way D-plug, the cable must be connected pin-to pin (i.e. Pin 1 to
Pin 1, Pin 2 to Pin 2 etc.). If the computer has a 9-way D-plug, a standard RS232 9-way
to 25-way cable is required.
The iTC does not require signals to be present on the RTS or DTR (pin 20) lines. The
RTS signal is fed back to the computer as CTS. The iTC sends logic high levels (+5 V)
to the computer on DSR and DCD.
Voltage levels for the transmitted and received data are listed in Table 4-4 .
Table 4-3 RS232 connections on the iTC
Pin Signal Name Notes
1 FG Linked to chassis ground inside the iTC.
2 TD Data from the computer to the iTC.
3 RD Data from the iTC to the computer.
4 RTS Linked to Pin 5 inside the iTC.
5 CTS Linked to Pin 4 inside the iTC.
6 DSR Linked to +5 V when the iTC is powered.
7 SG Linked to digital ground inside the iTC.
8 DCD Linked to +5 V when the iTC is powered.
9 to 25 Open circuit.
Table 4-4 RS232 voltage levels
Signal Allowed Voltage Level
Tx data high >+5.5 V
Tx data low <-5.5 V
Rx data high threshold <+2.6 V
Rx data low threshold >+1.4 V
Max Rx input voltage ±30 V