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Communications Processor (CP)
4-74
MC68302 USER’S MANUAL
MOTOROLA
the SCC mode register when that SCC is configured for HDLC. The read-write HDLC mode
register is cleared by reset.
NOF3–NOF0—Minimum Number of Flags between Frames or before Frames (0 to 15
Flags)
If NOF3–NOF0 = 0000, then no flags will be inserted between frames. Thus, the closing
flag of one frame will be followed immediately by the opening flag of the next frame in the
case of back-to-back frames.
C32—CRC16/CRC32
0 = 16-bit CCITT CRC (X16 + X12 + X5 + 1)
1 = 32-bit CCITT CRC (X32 + X26 + X23 + X22 + X16 + X12 + X11 + X10 + X8 + X7
+ X5 + X4 + X2 + X1 + 1)
FSE—Flag Sharing Enable
0 = Normal operation
1 = If NOF3–NOF0 = 0000, then a single shared flag is transmitted between back- to-
back frames. Other values of NOF3–NOF0 are decremented by one when FSE is
set. This is useful in Signaling System #7 applications.
Bit 9—Reserved for future use.
RTE—Retransmit Enable
0 = No automatic retransmission will be performed.
1 = Automatic retransmit enabled
Automatic retransmission occurs if a CTS lost condition happens on the first or second
buffer of the frame. See 4.5.12.8 HDLC Error-Handling Procedure.
FLG—Transmit Flags/Idles between Frames and Control the RTS Pin
0 = Send ones between frames; RTS is negated between frames. If NOF–NOF0 is
greater than zero, RTS will be negated for a multiple of eight transmit clocks. The
HDLC controller can transmit ones in both the NRZ and NRZI data encoding for-
mats. The CP polls the Tx BD ready bit every 16 transmit clocks.
1 = Send flags between frames. RTS is always asserted. The CP polls the Tx BD ready
bit every eight transmit clocks.
NOTE
This bit may be dynamically modified. If toggled from a one to a
zero between frames, a maximum of two additional flags will be
transmitted before the idle condition will begin. Toggling FLG will
never result in partial flags being transmitted.
15
14
13
12
11
10
9
8
7
6
5
0
NOF3 NOF2 NOF1 NOF0
C32
FSE
—
RTE
FLG
ENC
COMMON SCC MODE BITS