Communication Processor Module
MOTOROLA
MPC823e REFERENCE MANUAL
16-277
COMMUNICATION
16
SCCs
16.9.19.10 SCCx ASYNC HDLC COMMANDS.
You can program the CPM command
register (CPCR) with the following commands to transmit data. See
Section 16.2.6.1 CPM
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
SCCx 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 the buffer descriptor that is terminated by
examining the TBPTR entry in the SCCx parameter RAM table. However, no new buffer
descriptor is accessed for this channel.
•
GRACEFUL STOP TRANSMIT
—This command is not supported by the SCCx ASYNC
HDLC controller.
•
RESTART TRANSMIT
—This command reenables the transmission of characters on
the transmit channel and the SCCx 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 must 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 MPC823e protocols, the SCCx ASYNC HDLC controller does
not flush the FIFO because of the STOP TRANSMIT command. A maximum of
32 characters can be transmitted before an abort sequence. However, this can
be avoided by programming TFL to 1 in the GSMR_H register.
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