RS-232-C Interface SME
1038.6002.02 6A.6 E-12
Handshake
Software handshake
The software handshake with the XON/XOFF protocol controls data transmission. If the receiver wishes
to inhibit data entry, it sends XOFF to the transmitter. The transmitter then interrupts the data output
until it receives a XON. The same function is provided at the transmitter side (controller).
Note: Software handshake is not suitable for transmission of binary data. Use the hardware handshake.
Hardware handshake
In case of a hardware handshake the instrument signals that it is ready for reception via line DTR and
RTS. A logic 0 means "ready" and a 1 means "not ready". Whether the controller is ready for reception
or not is signalled to the instrument via lines CTS or DSR (see signal lines). The transmitter of the
instrument is switched on by a 0 and off by a 1. Line RTS remains active as long as the serial interface
is active. Line DTR controls whether the instrument is ready for reception or not.
Connection between instrument and controller
Connection of the instrument with the controller is via a so-called 0-modem cable. In this case, the data,
control and signalling lines have to be cross-connected. For a controller with a 9-pin or 25-pin connector
the following circuit diagram applies.
SME Controller SME Controller
9 pin 9 pin 9 pin 25 pin
1
2
3
4
5
6
7
8
9
-------------------------------------
------------RxD / TxD---------------
------------TxD / RxD---------------
------------DTR /DSR---------------
------------GND / GND-------------
------------DSR / DTR--------------
------------RTS / CTS--------------
------------CTS / RTS--------------
-------------------------------------
1
3
2
6
5
4
8
7
9
1
2
3
4
5
6
7
8
9
-------------------------------------
------------RxD / TxD---------------
------------TxD / RxD---------------
------------DTR /DSR---------------
------------GND / GND-------------
------------DSR / DTR--------------
------------RTS / CTS--------------
------------CTS / RTS--------------
-------------------------------------
8
2
3
6
7
20
5
4
22
Fig. A-3 Wiring of data, control and signalling lines for hardware handshake
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