User's Manual

SATELLINE-M3-TR1
User Guide, Version 3.0
28
6 TRANSPARENT DATA TRANSMISSION
6.1 Serial interface, data format
The SATELLINE-M3-TR1 radio modem serial interface uses an asynchronous data format. No
external synchronising 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.
One character to be transmitted will thus contain a start bit; the data bits (which define the
specific character in question); an optional parity bit and one or two stop bits. The overall length
of one character is therefore 10, 11 or 12 bits. This should be taken into account when
calculating the data throughput capability of a system. In other words, the number of start, stop
and parity bits must be considered. A useful rule of thumb is that at a data transfer speed of
9600 bps, the transmission of one character will require roughly one millisecond (1 ms).
Start Data Parity End
Asynchronous character data format
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:
DATA FORMAT
CHARACTER
CHARACTER LENGTH
8 bit, no parity, 1 stop bit
0110011001
10 bit
8 bit, even parity, 1 stop bit
01100110001
11 bit
8 bit, odd parity, 1 stop bit
01100110011
11 bit
8 bit, no parity, 2 stop bits
01100110011
11 bit
8 bit, even parity, 2 stop bits
011001100011
12 bit
8 bit, odd parity, 2 stop bits
011001100111
12 bit
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 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. This is especially useful where one part of the
system uses an RS-485 serial port and another part uses the RS-232 serial port. In other words,
radio modems may also be utilised as serial port adapters in addition to the more common role
of wireless data transfer.
The serial port settings can be changed in the Programming Mode.