Lexicon
MC-12 Serial Communications Protocol Printed on: 07/13/05
SERIAL PORT A PASSED
SERIAL PORT B PASSED
This message is displayed for about 2 seconds before entering normal operating mode. If no messages are
displayed, then both wrap tests failed.
6 Data Link Layer
The data link layer is used to define a transmission packet. The layer appends a header and tail that
encloses the transmitted application packet data. The data link header will contain the start of packet byte
and count of bytes to follow. The data link tail will contain the end of packet byte.
Data Link Header:
Byte Number Description Value
First Byte(0) Start of Packet (SOP) 0xF1
Byte(1) DLL Data Count nn
Application Header:
Byte(2) Command nn
Byte(3)
APP Data Count (number of application data bytes to
Follow)
nn
Application Data:
Byte(4) Data[0] nn
Byte(5) Data[1] nn
… Data[…] nn
Last Data Byte -1 Data[Data Count -1] nn
Data Link Tail:
Last Byte End of Packet (EOP) 0xF2
6.1 Errors
If the number of DLL data bytes received is the same as the data count and an EOP has not been received,
the MC-12 responds by transmitting a NAK packet with an error code DC_ERR_INVALID_PACKET.
The MC-12 then continues to look for a SOP byte and will not process the erroneous application packet.
The HOST can use this as an indicator to retransmit the corrupted packet.
In addition, each byte of a packet must be received sequentially and within the INTER_PACKET_TIME.
If any of the bytes within a packet transmission exceeds the INTER_PACKET_TIME, the MC-12 will
respond by transmitting a NAK packet with an error code DC_ERR_INVALID_PACKET. The MC-12
then continues to look for a SOP byte and will not process the erroneous application packet. The HOST
can use this as an indicator to retransmit the corrupted packet.
© 2005 Harman Specialty Group All rights reserved. 11 of 106
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