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Physical Layer Interface Controller (PLIC)
MCF5272 ColdFire
®
Integrated Microprocessor User’s Manual, Rev. 3
Freescale Semiconductor
13-7
Because the presentation of HDLC encoded data on the physical interface is lsb first, the lsb is
right-aligned in the transmit and receive shift register.
A D-channel byte is formed by concatenating two D bits from each of four frames. This data is also
right-aligned in the D-channel receive register as shown in
Figure 13-7. D-Channel HDLC Encoded and Unencoded Data.
13.2.3.4
D-Channel Unencoded Data
As with the B channel, a mechanism is provided to support incoming D channels containing unencoded
data, even though as of this document’s publication date, no communication protocols using unencoded
D-channel data are known.
As with unencoded (PCM encoded) B-channel data, it is assumed unencoded D-channel information is
presented on the physical line msb first. The msb is left-aligned in the transmit and receive shift register,
that is, the first bit received is aligned in the msb position through to the last received bit of a byte that is
aligned in the lsb position.
A D-channel byte is formed by concatenating two D bits from each frame over four consecutive frames as
shown in
. These 8 bits are also left-aligned in the D-channel receive register, that is, the first
two D-channel bits from the first frame go into the two msbs, B
7
and B
6
, the next two D-channel bits from
the second frame in B
5
and B
4
, and so on, until the last two D-channel bits in the fourth frame are aligned
in B
1
and B
0
.
DCL
FSR
Din/Dout
D
0
D
1
Frame 0
Frame 1
Frame
3
2
1
0
D7
D6
D5
D4
D3
D2
D1
D0
D
2
D
3
D
4
D
5
D
6
D
7
Frame 2
Frame 3
Din/Dout
D
7
D
6
D
5
D
4
D
3
D
2
D
1
D
0
Unencoded
HDLC
Encoded
8-Bit D-Channel Receive/Transmit Register, RD, TD