Async Hdlc Command Set; Transmit Commands - Motorola MC68360 User Manual

pins. A maskable interrupt may be generated upon a status change in either one of those
lines.

5.1 ASYNC HDLC Command Set

The following commands are issued to the Command Register (CR) documented in Section
7.1 of the MC68360 User's Manual.

5.1.1 Transmit Commands

After a hardware or software reset and the enabling of the channel in the SCC mode regis-
ter, the channel is in the transmit enable mode and starts polling the first BD in the table ev-
ery 8 transmit bit-times, or immediately if the TOD bit in the TODR is set.
STOP TRANSMIT Command
The STOP TRANSMIT command transmits the Asynchronous HDLC ABORT sequence
($7d, $7e) and then disables the transmission of data. If this command is received by the
ASYNC HDLC controller during frame transmission, the ABORT sequence will be placed
into the FIFO and the transmitter will not attempt to send any more data from the current Tx
BD. The controller does not advance to the next Tx BD. You can determine which BD was
terminated by examining the TBPTR entry in the SCC parameter RAM table. No new BD will
be accessed for this channel.
Unlike the other QUICC protocols, the Asynchronous HDLC
controller does not flush the FIFO due to the STOP TRANSMIT
command. Thus, up to 16 characters (32 on SCC1) may be
transmitted before the ABORT sequence is transmitted. This
can be avoided by programming TFL to 1 in the GSMR register.
GRACEFUL STOP TRANSMIT Command
This command is not supported by the Asynchronous HDLC controller.
RESTART TRANSMIT Command
The RESTART TRANSMIT command re-enables the transmission of characters on the
transmit channel. This command is expected by the ASYNC HDLC controller after a STOP
TRANSMIT command or after a transmitter error. The ASYNC HDLC controller will resume
transmission from the first character in the current transmitter BD (TBPTR) in the channel's
transmit BD table.
INIT TX PARAMETERS Command
Initializes all the transmit parameters in this serial channel's parameter RAM to their reset
state. This command must be issued before the transmitter is enabled for the first time. This
command should only be issued when the transmitter is disabled. Note that the INIT TX
AND RX PARAMETERS command may also be used to reset both transmit and receive pa-
rameters.
MOTOROLA
Freescale Semiconductor, Inc.
Note
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Asynchronous HDLC
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