Transparent Data Transmission
13
SRL-35 Operator’s Manual P/N: 1003224-01
Transparent Data Transmission
Serial Interface, Data Format
The SRL-35 serial interface uses an asynchronous data format. No external synchronizing signal is needed, since
necessary timing information is acquired from the start and stop bits transmitted before and after each data
field bits (byte).
The data transfer speed of the serial interfaces can be set to 300, 600, 1200, 2400, 4800, 9600, 19200 or 38400
bps (bits per second). The length of the data field must be 7, 8 or 9 bits. When using a data field length of 7 or
8 bits, a parity bit may also be used.
Example:
With an 8-bit data character length and taking, for example, a decimal value of ”204”, (which
corresponds to a binary value of ”11001100”) and with a start bit value of ”0”, parity bit set to either “NO”
(NONE), ”0” or ”1” and with a stop bit value of ”1”, the possible combinations are listed in the table below:
If the settings of data speed, character length, parity or the number of stop bits differ between the radio
modem and the terminal, errors will be introduced into the transferred data. The serial port settings of each
individual radio modem in a system can all be different apart from the data length setting (7, 8 or 9 bits), which
must always be the same in each individual radio data modem. In other words, the serial port used, the data
transfer speed, parity and number of stop bits; can be different in different parts of a same system. The serial
port settings can be changed in the Programming Mode.
Serial interface settings of the modem and terminal device connected to it must match.
Handshake Lines
When using the RS-232 serial interface, handshake signals can be used to control data transfer. Handshake
signals are used, for example, by the radio modem to inform the terminal that the radio channel is busy, and
that it cannot initiate transmission. The terminal can also control the radio modem via RTS-line.
A common way of using handshaking signals is to monitor the CTS-line and ignore the others. Usually the
terminal is fast enough to handle the data received by the radio modem, so the use of RTS-line is not necessary.
Handshaking is not needed if the system protocol is designed to prevent collisions (data contention) by the use
of polling, or if there is little traffic and also if there is no harm from occasional data contention situations
(several radio modems try to transmit at the same time).
Table 12. Handshake Lines
Line Direction
CTS To termina l
RTS To modem
CD To termina l
To Next Page
Loading...
