SECTION 3: DATA COMMUNICATIONS InSpec Sampler Controller
3.9 THE RIGHT CONNECTION
The following is based on a simple RS232 connection.
• Two terms that recur in data communications are DTE (Data Terminal Equipment) and DCE (Data
Communication Equipment).
• Computers and terminals are usually DTE’s, modems and communications hardware are generally
DCE’s while other equipment such as multiplexers and printers can be either.
• DTE’s transmits and receive on different pins in the connector than DCE’s.
• Therefore, to avoid common errors when connecting equipment it is important to know the definition
of the particular item of equipment.
• If you connect a DTE with a DCE, the DTE will transmit data on pin 2 while the DCE will receive
data on pin 2 (in spite of the fact that the signal name is the same in both cases). This can be
achieved with a ‘straight through’ type cable.
• If you connect to DTE’s, you have to connect pin 2 and pin 3 in order for the transmitter to be
connected to the receiver. This can be achieved with a ‘null modem’ type cable.
1
DCD
2
Rx
3
Tx
4
DTR
5
GND
6
DSR
7
RTS
8
CTS
9
RI
DTE
1
DCD
2
Rx
3
Tx
4
DTR
5
GND
6
DSR
7
RTS
8
CTS
9
RI
DTE
1
DCD
2
Rx
3
Tx
4
DTR
5
GND
6
DSR
7
RTS
8
CTS
9
RI
DTE
1
DCD
2
Rx
3
Tx
4
DTR
5
GND
6
DSR
7
RTS
8
CTS
9
RI
DCE
Minimum Null Modem Cable
For 9 Way D-Type Connection
Minimum Straight Cable
For 9 Way D-Type Connection
Figure 30 - Communications Cable Build
The InSpec debug communications port uses a DTE connection and a cross cable will be required to
connect and debug the instrument.
3.10 RS232
EIA-232 or RS232 is perhaps the most common interface for data communications via a 9 or 25-pin D-
type connector serial port V.24 standard.
The V.24 standard recommends that the cable should be no longer than 15 metres. V.24 (the CCITT
standard) or RS-232-C (the EIA standard) are two standards which are similar, in principle, and for most of
applications can be treated as the same. V.24 is the physical standard that defines how units should be
connected to each other and this also defines the appearance of the connector. V.28 is the electrical standard.
For this reason, the interface is sometimes described as V.24/V.28.
The InSpec serial ports support RS232 on all of it serial communication ports.
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