Freescale Semiconductor MPC8260 - Manual (Page 733)

SCC HDLC Mode
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 22-5
address comparisons. Receive errors are reported through the RxBD; transmit errors are reported through
the TxBD.
22.6 SCC HDLC Commands
The transmit and receive commands are issued to the CP command register (CPCR). Transmit commands
are described in
Table 22-2 .
Receive commands are described in Table 22-3 .
22.7 Handling Errors in the SCC HDLC Controller
The SCC HDLC controller reports frame reception and transmission errors using BDs, error counters, and
the SCCE. Transmission errors are described in
Table 22-4 .
Table 22-2. Transmit Commands
Command Description
STOP
TRANSMIT
After a hardware or software reset and a channel is enabled in the GSMR, the transmitter starts polling
the first BD in the TxBD table every 64 Tx clocks, or immediately if TODR[TOD] = 1, and begins sending
data if TxBD[R] is set. If the SCC receives the
STOP TRANSMIT command while not transmitting, the
transmitter stops polling the BDs. If the SCC receives the command during transmission, transmission
is aborted after a maximum of 64 additional bits, the Tx FIFO is flushed, and the current BD pointer
TBPTR is not advanced (no new BD is accessed). The transmitter then sends an abort sequence (0x7F)
and stops polling the BDs.
When not transmitting, the channel sends flags or idles as programmed in the GSMR.
Note that if PSMR[MFF] = 1, multiple small frames could be flushed from the Tx FIFO; a
GRACEFUL STOP
TRANSMIT command prevents this.
GRACEFUL
STOP
TRANSMIT
Stops transmission smoothly. Unlike a STOP TRANSMIT command, it stops transmission after the current
frame is finished or immediately if no frame is being sent. SCCE[GRA] is set when transmission stops.
HDLC Tx parameters and Tx BDs can then be updated. TBPTR points to the next TxBD. Transmission
begins once TxBD[R] of the next BD is set and a
RESTART TRANSMIT command is issued.
RESTART
TRANSMIT
Enables frames to be sent on the transmit channel. The HDLC controller expects this command after a
STOP TRANSMIT is issued and the channel in its GSMR is disabled, after a GRACEFUL STOP TRANSMIT
command, or after a transmitter error. The transmitter resumes from the current BD.
INIT TX
PARAMETERS
Resets the Tx parameters in the parameter RAM. Issue only when the transmitter is disabled. INIT TX
AND RX PARAMETERS resets both Tx and Rx parameters.
Table 22-3. Receive Commands
Command Description
ENTER HUNT
MODE
After a hardware or software reset, once an SCC is enabled in the GSMR, the receiver is automatically
enabled and uses the first BD in the RxBD table. While the SCC is looking for the beginning of a frame,
that SCC is in hunt mode. The
ENTER HUNT MODE command is used to force the HDLC receiver to stop
receiving the current frame and enter hunt mode, in which the HDLC continually scans the input data
stream for a flag sequence. After receiving the command, the buffer is closed and the CRC is reset.
Further frame reception uses the next BD.
CLOSE RXBD Should not be used in the HDLC protocol.
INIT RX
PARAMETERS
Resets the Rx parameters in the parameter RAM.; issue only when the receiver is disabled. Note that
INIT TX AND RX PARAMETERS resets both Tx and Rx parameters.