MPC8280 datasheet(759/1386 Pages) FREESCALE

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SCC BISYNC Mode

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

23-5

Receive commands are described in Table 23-3.

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.

Table 23-2. Transmit Commands

Command

Description

STOP TRANSMIT

After hardware or software is reset and the channel is enabled in the GSMR, the channel is in

transmit enable mode and starts polling the first BD every 64 transmit clocks. This command stops

transmission after a maximum of 64 additional bits without waiting for the end of the buffer and the

transmit FIFO to be flushed. TBPTR is not advanced, no new BD is accessed, and no new buffers

are sent for this channel. SYNC–SYNC or DLE–SYNC pairs are sent continually until a RESTART

TRANSMIT

is issued. A STOP TRANSMIT can be used when an EOT sequence should be sent and

transmission should stop. After transmission resumes, the EOT sequence should be the first buffer

sent to the controller.

Note that the controller remains in transparent or normal mode after it receives a STOP TRANSMIT or

RESTART TRANSMIT

command.

GRACEFUL STOP

TRANSMIT

Stops transmission after the current frame finishes sending or immediately if there is no frame being

sent. SCCE[GRA] is set once transmission stops. Then BISYNC transmit parameters and TxBDs

can be modified. The TBPTR points to the next TxBD. Transmission resumes when the R bit of the

next BD is set and a RESTART TRANSMIT is issued.

RESTART

TRANSMIT

Lets characters be sent on the transmit channel. The BISYNC controller expects it after a STOP

TRANSMIT

or a GRACEFUL STOP TRANSMIT command is issued, after a transmitter error occurs, or after

a STOP TRANSMIT is issued and the channel is disabled in its SCCM. The controller resumes

transmission from the current TBPTR in the channel’s TxBD table.

INIT TX

PARAMETERS

Initializes all transmit parameters in the serial channel’s parameter RAM to their reset state. Issue

only when the transmitter is disabled. INIT TX AND RX PARAMETERS resets transmit and receive

parameters.

Table 23-3. Receive Commands

Command

Description

RESET BCS

CALCULATION

Immediately resets the receive BCS accumulator. It can be used to reset the BCS after recognizing

a control character, thus signifying that a new block is beginning.

ENTER HUNT

MODE

After hardware or software is reset and the channel is enabled in SCCM, the channel is in receive

enable mode and uses the first BD. This command forces the controller to stop receiving and enter

hunt mode, during which the controller continually scans the data stream for an SYN1–SYN2

sequence as programmed in the DSR. After receiving the command, the current receive buffer is

closed and the BCS is reset. Message reception continues using the next BD.

CLOSE RXBD

Used to force the SCC to close the current RxBD if it is in use and to use the next BD for subsequent

data. If data is not being received, no action is taken.

INIT RX

PARAMETERS

Initializes receive parameters in this serial channel’s parameter RAM to reset state. Issue only when

the receiver is disabled. An INIT TX AND RX PARAMETERS resets transmit and receive parameters.

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