User's Manual
Chapter Three Operation
Man_905UD_2.0.doc Page 17
3.2 Serial and Radio Data
Data input at the serial port is placed into the input buffer. This buffer will store 8Kbytes of
data, and CTS control is provided on the RS232 port to prevent overflow.
When the 905U-D unit detects data in the input buffer, it initiates a radio message. The radio
message will end when the number of transmitted bytes reaches the maximum message
length (configurable by the user). The message will also end if the input buffer becomes
empty, however the radio transmitter will remain active for a delay time in case more bytes
are input at the serial port. The delay time is called the “tail time” and is configurable by the
user.
3.2.1 Character Type
The 905U-D may be configured by the user to recognise the following types of characters.
Data
Bits
Start
Bits
Stop
Bits Parity
7 1 1 even
7 1 1 odd
7 1 2 none
7 1 2 even
7 1 2 odd
8 1 1 none
8 1 1 odd
8 1 1 even
8 1 2 none
Most applications will require the character type to be the same at each 905U-D
modem in the system. Nevertheless, the character type may be configured to be
different at different 905U-D modems. Data is transmitted by radio as an eight-bit
byte without stop or start bits. If the input data is 7 data bits without parity, then the
byte transmitted by radio comprises the 7 bits plus a zero bit. If the input data is 7
data bits with parity, then the byte transmitted comprises the same byte. Input
characters with 8 bits are transmitted as just the 8 data bits, with no parity. Because
the data may be transmitted without parity, the user may configure CRC error
checking to be added to each transmitted data packet. Data is output at the
destination module based on the character type configured at that module - that is,
the start/stop bits and parity is added to the radio data.3.2.2 Serial Data Rate
The communications baud rates supported on both the RS232 serial port and the RS485
serial port are 1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200 baud - the user
selects one of these rates during the configuration of the modem.