Information

45.4.1.1 CEA709.1-B packet cycle
The following figure illustrates the frame format and Differential Manchester encoding.
Differential Manchester encoding requires that each transmitted bit includes a clock
transition at the start of the bit period. This allows synchronization with the receiver.
1
1
0
1
1
0
1
0
Bit Sync
Byte
Sync
Data+16bit CRC Line
Code
Beta1 SDT
Transmitter Enable
Figure 45-193. Frame format with differential manchester encoding
A logic zero is indicated with the presence of a transition in the middle of the bit period
and a logic one is indicated by the absence of any transition. When transitions occur at
the start of the bit time, polarity is arbitrary because the last bit of a transmission has no
trailing clock edge. A transmitter will transmit a preamble at the beginning of a packet to
allow other nodes to synchronize their receiver clocks. The preamble comprises a bit-
sync field followed by a byte-sync field. The bit-sync field is a series of differential
Manchester logic ones and the byte-sync field is a single differential Manchester logic
zero. The byte-sync field marks the end of the preamble and the start of the data field
(MPDU/LPDU).
The transmitter terminates the packet by forcing the data output to be transitionless long
enough for the receiver to recognize an invalid bit code. This signals the end of the
packet. At the end of the packet transmission, the line must remain transitionless for three
bit periods after the final clock transition.
The UART is responsible for providing the BitSync and ByteSync fields of the PPDU
illustrated below. The layer two software manages all other encapsulating fields and
provides these to the UART as part of the packet to be transmitted.
Byte Sync
Priority
Alt Path Delta BL
CRC
NPDU
Bit Sync
Figure 45-194. Physical protocol data unit structure
Functional description
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
1098 Freescale Semiconductor, Inc.