Motorola MPC8260 - Manual (Page 638)

22-6 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA
Part IV. Communications Processor Module
22.6 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 deÞned 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 deÞnes classes of control characters that support masking option.
Offset from
SCCx Base 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0x42 E B H Ñ CHARACTER1
0x44 E B H Ñ CHARACTER2
0x46 E B H Ñ CHARACTER3
0x48 E B H Ñ CHARACTER4
0x4A E B H Ñ CHARACTER5
0x4D E B H Ñ CHARACTER6
0x4E E B H Ñ CHARACTER7
0x50 E B H Ñ CHARACTER8
0x52 1 1 1 Ñ MASK VALUE(RCCM)
Figure 22-2. Control Character Table and RCCM