SATELLINE-3AS and SATELLINE-3ASd
17
5.2
5.2
Data Transmission (RS-interface)
Data Transmission (RS-interface)
5.2.1
Data format
The SATELLINE-3AS radio modem uses asynchronous data format. Asynchronous transmission
does not require a continuous synchronising signal from the transmitter to the receiver. The data
bits of each character are preceded by a start bit and followed by one or two stop bits. They are
inserted after the data bits to provide a minimum period between characters.
Standard data bit rates for SATELLINE-3AS are 300, 600, 1200, 2400, 4800, 9600, 19200
and 38400 bps (bits per second).
The length of the data field should be 7, 8 or 9 bits. If the data length is 9 bits, the selection of
parity has to be NONE.
When a parity bit is used, its logic state depends on the specific character code and whether the
agreed protocol specifies even parity or odd parity. The parity bit is simply made 1 or 0, as
required, to make the total number of 1s in the data an even (even parity) or an odd (odd parity).
Note that the parity bit itself is included in the count, but the stop bit or stop bits are excluded.
The whole character length includes start bit, data bits, parity bit and stop bit or bits. The
character length is 10, 11 or 12 bits.
Start
Data
Parity Stop
Asynchronous data format
Example: 8 bit data value is 204 ( 11001100 binary ), start bit is 0, parity is none, 0 or 1and
stop bit 1.
The possible characters are:
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
It can be seen that there are always 2, 3 or 4 extra bits per one data word, that must be taken
into account when calculating the system throughput.
If the data speed, character length, parity or the number of stop bits are incorrectly set, errors will
appear in transmission. At reception they appear as "error characters" or as an incorrect
operation of the modem.
