Interfaces
R&S®SML / R&S®SMV03
1090.3123.12
E-6
5.30
Handshake
Software handshake
The software handshake with the XON/XOFF protocol controls data transmission.
If the receiver (instrument) wishes to inhibit the input of data, it sends XOFF to the transmitter. The
transmitter then interrupts data output until it receives XON from the receiver. The same function is also
provided at the transmitter end (controller).
Note:
The software handshake is not suitable for the transmission of binary data. Here the
hardware handshake is to be preferred.
Hardware handshake
With a hardware handshake, the instrument signals its readiness for reception via the lines DTR and
RTS. A logic 0 means "ready", a logic 1 means "not ready".
Whether or not the controller is ready for reception is signalled to the instrument via the CTS or the DSR
line (see section "Signal Lines"). The transmitter of the instrument is switched on by a logic 0 and off by
a logic 1. The RTS line remains active as long as the serial interface is active. The DTR line controls the
instrument’s readiness for reception.
Wiring between instrument and controller
Wiring between the instrument and the controller is by means of a null modem, ie the data, control and
signalling lines have to be cross-connected. The wiring plan below applies to controllers with a 9-pin or
25-pin connector.
R&S SML / R&S SMV03
Controller
R&S SML / R&S SMV03
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. 5-7
Wiring of data, control and signalling lines for hardware handshake
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