Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 744

Powerquicc family

Table of Contents

SCC BISYNC Mode

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 easily be 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.

Figure 26-2. Control Character Table and RCCM

MPC885 PowerQUICC Family Reference Manual, Rev. 2

MASK VALUE(RCCM)

Freescale Semiconductor