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Danish Interpretation Systems Technical Specifications
Printed in Denmark
8
3 Serial Protocol
All communication between the CU and the external control unit is done through a serial connection
either via RS232 or RS422. The format of the serial data is 8 data bits, 1 stop bit and no parity.
Possible bit rates are 2400, 4800, 9600, 19200, 38400, 57600 and 115200 bits/s. The default is 115200
bits/s. Hardware flow control is used on the serial port.
The CU provides a possibility to save the settings in a configuration. Whenever the CU powers up, the
settings stored in the configuration are applied. The bit rate setting is part of the configuration, and is
applied after power up.
3.1 Package format
Communication between the CU and an external control unit consists of binary packages (messages).
Each binary message consists of bytes. The format of the packages sent between the CU and the
external control unit is as follows:
<START> <Message Type> <ID> <Data Byte 0> . . . <Data Byte N> <CRC> <STOP>
START is the constant 0xFC that indicates the start of a message
Message Type is a byte indicating the type of the message. The message types used is described in
section 3.4.
ID is a byte identifying this message in a stream of messages. Each time a message is sent this number
is incremented. When the maximum allowed value, 63, is reached the counter is wrapped. Separate
counters are used for message from the CU and messages to the CU.
Data byte 0 – Data byte N is the actual message to be sent.
CRC is an 8-bit CRC value for the message. The CRC is calculated over the bytes between the Start
and CRC. The calculation is described in section 3.2.
STOP is the constant 0xFD that indicates the end of a message.