
Communication Processor Module
16-270
MPC823 USER’S MANUAL
MOTOROLA
SCC2
COMMUNICATION
16
PROCESSOR
MODULE
16.9.19.10 SCC2 ASYNC HDLC COMMANDS. You can program the CPM command
Command Register for additional information. After the hardware or software is reset and
the channel is enabled by the SCCM–ASYNC HDLC register, the channel is in transmit
enable mode and starts polling the first buffer descriptor in the table every eight transmit bit
times or immediately if the TOD bit of the TODR is set.
STOP TRANSMIT—This command transmits the asynchronous HDLC abort sequence
(PPP–0x7D ;0x7E, IrLAP–0x7D ;0xC1) and disables the transmission of data. If the
ASYNC HDLC controller receives this command during frame transmission, the abort
sequence is put into the FIFO and the transmitter does not try to send any more data
from the current TX buffer descriptor. The controller also does not advance to the next
TX buffer descriptor. You determine which buffer descriptor is terminated by examining
the TBPTR entry in the SCC2 parameter RAM table. However, no new buffer descriptor
is accessed for this channel.
GRACEFUL STOP TRANSMIT—This command is not supported by the SCC2 ASYNC
HDLC controller.
RESTART TRANSMIT—This command reenables the transmission of characters on
the transmit channel and the SCC2 ASYNC HDLC controller expects it after a STOP
TRANSMIT command or transmitter error. The controller continues transmitting from
the first character in the current transmitter buffer descriptor in the channel’s transmit
buffer descriptor table.
INIT TX PARAMETERS—This command initializes all the transmit parameters in this
serial channel’s parameter RAM to their reset state. It must be issued before the
transmitter is enabled and should only be issued when the transmitter is disabled. The
INIT TX AND RX PARAMS command can also be used to reset the transmit and
receive parameters.
Note: Unlike the other MPC823 protocols, the SCC2 ASYNC HDLC controller does not
flush the FIFO because of the STOP TRANSMIT command. Up to 32 characters
can be transmitted ahead of the abort sequence. However, this can be avoided
by programming TFL to 1 in the GSMR_H register.