Communications Processor (CP)
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MC68302 USER’S MANUAL
MOTOROLA
If in-line synchronization is used with the transparent controller, then the DSR (see 4.5.4
SCC Data Synchronization Register (DSR)) must be initialized with the SYN1–SYN2 syn-
chronization characters. See 4.5.16.5 Transparent Synchronization for details.
4.5.16.4 Transparent Commands
The following commands are issued to the command register.
STOP TRANSMIT Command
After a hardware or software reset and the enabling of the channel using the SCC mode
register, the channel is in the transmit enable mode and starts polling the first BD in the
table approximately every 16 transmit clocks.
The STOP TRANSMIT command aborts transmission. If this command is received by the
transparent controller during a buffer transmission, transmission of that buffer is aborted
after the FIFO contents (up to four words) are transmitted. The TBD# is not advanced.
Ones are continuously transmitted until transmission is re-enabled by issuing the RE-
START TRANSMIT command.
The STOP TRANSMIT command must be issued before the SCC mode register is used
to disable the transmitter if the transmitter is to be re-enabled at a later time.
RESTART TRANSMIT Command
The RESTART TRANSMIT command is used to begin or resume transmission from the
current Tx BD number (TBD#) in the channel's Tx BD table. When this command is re-
ceived by the channel, it will start polling the ready bit in this BD. This command is expect-
ed by the transparent controller after a STOP TRANSMIT command, after a STOP
TRANSMIT command and the disabling of the channel in its mode register, or after a
transmitter error (underrun or CTS lost occurs).
If the transmitter is being re-enabled, the RESTART TRANSMIT command must be used
and should be followed by the enabling of the transmitter in the SCC mode register.
ENTER HUNT MODE Command
After a hardware or software reset and the enabling of the channel in the SCC mode reg-
ister, the channel is in the receive enable mode and will use the first BD in the table.
The ENTER HUNT MODE command is used to force the transparent controller to abort
reception of the current block, generate an RX interrupt (if enabled) as the buffer is closed,
and enter the hunt mode. In the hunt mode, the transparent controller waits for a synchro-
nization to occur on the SCC (see 4.5.16.5 Transparent Synchronization). After receiving
the ENTER HUNT MODE command, the current receive buffer is closed. Reception con-
tinues using the next BD.
If an enabled receiver has been disabled (by clearing ENR in the SCC mode register), the
ENTER HUNT MODE command must be given to the channel before setting ENR again.
4.5.16.5 Transparent Synchronization
Once the SCC is enabled for transparent operation in the SCM, the transmit and receive
buffer descriptors are made ready for the SCC, and the transmit FIFO has been preloaded
by the SDMA channel (signaled by the RTS pin in NMSI and PCM modes), one additional
process must occur before data can be transmitted and received. This process is called