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M&C Serial Protocol.
SCI Packet Byte Description
♦
STX
is the start transmission byte (defined as 0x7E). This byte is used to determine the start of a packet.
♦
Dest/Src Address
contains the destination address in the high nibble and the source address in the low
nibble. The destination address is the address of the device which is to process the packet. The source
address is the address of the device which sent the packet. Note that the device address of the customer
interface device is always = 0x0F.
♦
CMD/Len
contains the packet command in the high nibble and the number of bytes in the data portion of
the packet in the lower nibble.
The following commands may be sent by the customer interface device:
GET (command high nibble = 0x0) Request the current value of a database element.
SET (command high nibble = 0x1) Set the database element to the specified value.
The following commands may be returned to the customer interface device:
UPD (command high nibble = 0x8) Return the current value of a database element.
ACK (command high nibble = 0xE) Acknowledge a received packet.
NACK (command high nibble = 0xF) Reject a received packet (Not ACKnowledge).
♦
Data1 - Datan
contains the packet payload. The value of the data bytes is specific to the command and will be
covered in following sections.
♦
CRC
is the cyclic redundancy check and is calculated by performing a byte-wise exclusive OR of the
Dest/Src address byte, Cmd/Len byte and all data bytes. A bit-wise inversion is then applied to the CRC
before being inserted into the packet.
♦
ETX
is the end transmission byte (defined as 0x7F). This byte is used to determine the end of a packet.
Default Address Values
The customer interface device must always be assigned address 0xF.
The Transceiver device address is factory defaulted to 0xF. It may be set by the customer using the SET Transceiver
Address command (refer to SET Control Command List).
The Booster device address is factory defaulted to 0xE. It may be set by the customer using the SET Booster
Address command (refer to SET Control Command List).
Command / Reply Packet Sequencing
The Transceiver will never send a packet to the customer interface device unless a command is received. In other
words, the Transceiver will not speak unless spoken to.
Default Reply Packet Format
This section identifies the packet format the ACK (Acknowledge) and NACK (Not acknowledge) replies which may
be sent to the customer interface device in response to a received command.
