
GT-96100A Advanced Communication Controller
Revision 1.0
339
14.5.3 MPSCx Protocol Configuration Register (MPCRx) for HDLC
Figure 61: MPSCx Protocol Configuration Register (MPCRx) for HDLC
Table 326: MPSCx Protocol Configuration Register (MPCRx) for HDLC, Offset: 0x000A08,
0x008A08, 0x010A08, 0x018A08, 0x020A08, 0x028A08, 0x030A08, 0x038A08
(where x is the port number 0 to 7)
Bits
Field
Name
F unctio n
In itial
Valu e
1:0
Reserved.
0
2
LCT
Local Talk
When set, the following LocalTalk support is added to the HDLC controller:
Two abort sequences will be generated at the end of frame follow-
ing its closing flag.
A preamble will be generated. No encoding will be done for the last
preamble bit
When working with LocalTalk, the FM0 Encoding Scheme should be set by
writing ‘010’ to RENC and TDEC in the MMCRx. The user should also set
TPPT to 0xF and TPL to ‘1’ (one byte preamble). The last preamble bit is not
decoded. This must be done for LocalTalk RTS frames. Setting TPL to ‘0’
leads to a frame without preamble. This can be used with LocalTalk data
frames. Setting TPL to other values leads to unpredictable results.
0
3
Reserved.
0
4
CCM
CRC Compliance Mode.
In HDLC, the TX side uses bit stuffing to prevent a data/CRC pattern from
looking like an HDLC control flag. The CCM tells the Rx side how to handle
frames that were received with mistakes in bit stuffing, when they occur
immediately before the end flag. This is a borderline condition that may or
may not present a problem in actual systems.
0 - Compatible Mode. If the Rx side receives a frame that is missing a
stuffed bit that is supposed to be immediately before the End Flag, then
mark in the descriptor that the frame has a good CRC, and pass the good
CRC along to the buffer.
1 - Compliance Mode. If the Rx side receives a frame that is missing a
stuffed bit that is supposed to immediately proceed the End Flag, then mark
in the descriptor that the frame has a bad CRC, and pass the errored CRC
to the buffer.
5
Reserved.
0
3
1
3
0
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
1
2
0
1
9
1
8
1
7
1
6
1
5
1
4
1
3
1
2
1
09 8 765 4 3210
Base + 08
MPCRx
NOF
CL
M
DR
T
LC
T
CCM