Motorola PowerQUICC II MPC8280 Series Reference Manual page 798

SCC BISYNC Control Character Recognition
23.6 SCC BISYNC Control Character Recognition
The BISYNC controller recognizes special control characters that customize the protocol
implemented by the BISYNC controller and aid its operation in a DMA-oriented
environment. They are used for receive buffers longer than one byte. In single-byte buffers,
each byte can be easily inspected so control character recognition should be disabled.
The control character table lets the BISYNC controller recognize the end of the current
block. Because the controller imposes no restrictions on the format of BISYNC blocks,
software must respond to received characters and inform the controller of mode changes
and of certain protocol events, such as resetting the BCS. Using the control character table
correctly allows the remainder of the block to be received without interrupting software.
Up to eight control characters can be defined to inform the BISYNC controller that the end
of the current block is reached and whether a BCS is expected after the character. For
example, the end-of-text character (ETX) implies an end-of-block (ETB) with a subsequent
BCS. An enquiry (ENQ) character designates an end of block without a subsequent BCS.
All the control characters are written into the data buffer. The BISYNC controller uses a
table of 16-bit entries to support control character recognition. Each entry consists of the
control character, an end-of-table bit (E), a BCS expected bit (B), and a hunt mode bit (H).
The RCCM entry defines classes of control characters that support masking option. The
control character table and RCCM are shown in Figure 23-2.
Offset from
SCCx Base
0 1
0x42 E B
0x44 E B
0x46 E B
0x48 E B
0x4A E B
0x4D E B
0x4E E B
0x50 E B
0x52 1 1
Figure 23-2. Control Character Table and RCCM
23-6
Freescale Semiconductor, Inc.
2 3
H —
H —
H —
H —
H —
H —
H —
H —
1 —
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7 8
CHARACTER1
CHARACTER2
CHARACTER3
CHARACTER4
CHARACTER5
CHARACTER6
CHARACTER7
CHARACTER8
MASK VALUE(RCCM)
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