Motorola MPC860 PowerQUICC, User Manual

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MOTOROLA Chapter 24. SCC HDLC Mode 24-7
Part V. The Communications Processor Module
24.8 HDLC Mode Register (PSMR)
The protocol-speciÞc mode register (PSMR), shown in Figure 24-4, functions as the HDLC
mode register.
Table 24-6 describes PSMR HDLC Þelds.
Abort
Sequence Occurs when seven or more consecutive ones are received. When this occurs while receiving a frame,
the channel closes the buffer, sets RxBD[AB] and generates a maskable RXF interrupt. The channel
also increments the abort sequence counter ABTSC. The CRC and nonoctet error status conditions
are not checked on aborted frames. The receiver then enters hunt mode.
Nonoctet
Aligned
Frame The channel writes the received data to the buffer, closes the buffer, sets RxBD[NO], and generates a
maskable RXF interrupt. CRC error status should be disregarded on nonoctet frames. After a nonoctet
aligned frame is received, the receiver enters hunt mode. An immediate back-to-back frame is still
received. The nonoctet data may be derived from the last word in the buffer as follows:
Note that if buffer swapping is used (RFCR[BO] = 0b0x), the Þgure above refers to the last byte, rather
than the last word, of the buffer. The lsb of each octet is sent Þrst while the msb of the CRC is sent Þrst.
CRC The channel writes the received CRC to the buffer, closes the buffer, sets RxBD[CR], generates a
maskable RXF interrupt, and increments the CRC error counter CRCEC. After receiving a frame with
a CRC error, the receiver enters hunt mode. An immediate back-to-back frame is still received. CRC
checking cannot be disabled, but the CRC error can be ignored if checking is not required.
Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Field NOF CRC RTE Ñ FSE DRT BUS BRM MFF Ñ
Reset 0
R/W R/W
Address 0xA08 (PSMR1), 0xA28 (PSMR2), 0xA48 (PSMR3), 0xA68 (PSMR4)
Figure 24-4. HDLC Mode Register (PSMR)
Table 24-6. PSMR HDLC Field Descriptions
Bits Name Description
0-3 NOF Number of ßags. Minimum number of ßags between or before frames. If NOF = 0b0000, no ßags are
inserted between frames and the closing ßag of one frame is followed by the opening ßag of the next
frame in the case of back-to-back frames. NOF can be modiÞed on-the-ßy.
4Ð5 CRC CRC selection.
00 16-bit CCITT-CRC (HDLC). X16 + X12 + X5 + 1.
x1 Reserved.
10 32-bit CCITT-CRC (Ethernet and HDLC). X32 + X26 + X23 + X22 + X16 + X12 + X11 + X10 + X8 +
X7 + X5 + X4 + X2 + X1 +1.
Table 24-5. Receive Errors (Continued)
Error Description
msb lsb
1 0 0
Valid Data Nonvalid Data
Fi 24 3