User's Manual

Elpro Technologies E2-450 Radio Module Instruction Manual
6 www.cooperbussmann.com/wirelessresources Rev Version
1.0
2.1 Alternate Host Interface
The alternate host interface port provides similar signals to the main host interface. This port may be used for future
development.
2.2 Production Interfaces
The production interfaces consists of JTAG ports and serial interfaces directly to microcontrollers. These interfaces
are used in production and development only.
CHAPTER 3 - OPERATION
The host system communicates with the E2-450 module via the serial interface provided by the main host interface.
The serial interface is a standard TTL UART interface in full duplex asynchronous connection. The baud rate is
1.0Mbps. RTS and CTS lines are used to provide flow control between the host and radio processors.
The serial protocol is a proprietary message structure.
MessageFraming
Message framing is based on PPP Byte stuffing. The special characters 0x7F, 0x7D and 0xFF are the beginning of a
frame, data link escape and end of frame characters respectively.
Each message begins with the transmission of the start of frame character. This is followed by the message data
payload for the message end of the message is indicated by the end of frame character.
Occurrence of the characters for start of frame, end of frame, or the data link escape character within the data packet
is indicated by stuffing an additional data link escape character into the data stream before the special character and
then setting bit 5 of the control character to 0.
Whenever the start flag character is detected, the framer state is reset to receiving the first data payload byte. (Start
flag should never occur in the data payload due to the escaping scheme above.)
The end of frame character ensures that the transmitter and receiver are synchronised at the beginning of the next
data frame. If they are not correctly synchronised, the 0xFF will result in the additional “ones” being detected as a long
stop condition at the receiver and subsequent characters being correctly synchronised.
MessageFormat
Endian
All multi-byte fields are transmitted in little endian format.
GeneralMessageFormat
Table 1 describes the general format of the messages including the start and end flags.
START_FLAG 1 byte Start of message identifier (0x7E)
Service_code 2 bytes Service code to identify message type and message ID
Payload Data 0-n bytes Message payload data. Interpreted according to Service code
END_FLAG 1 byte End of message identifier (0xFF)
Table 1: General message format