Communication Processor Module
MOTOROLA
MPC823 USER’S MANUAL
16-193
SCC2
COMMUNICATION
16
PROCESSOR
MODULE
16.9.14 Disabling the SCC2 On-the-Fly
If you do not need the serial communication controller for a while, you can disable it and
reenable it later by following a sequence of steps, which ensures that any buffers currently
in use are properly closed and that new data is transferred to or from a new buffer. This
sequence must be followed if you are changing a parameter that cannot be dynamically
changed. Parameters that are dynamic can be changed immediately. For instance, the
internal baud rate generators allow on-the-fly changes, but the DPLL-related bits in the
GSMR_L do not.
16.9.14.1 DISABLING THE ENTIRE SCC2 TRANSMITTER. The SCC2 transmitter can
be fully disabled or enabled by following these steps:
1. Issue the STOP TRANSMIT command to the CPCR if the serial communication
controller is currently transmitting data. It should stop smoothly. If the serial
communication controller is not transmitting, then you do not need the STOP
TRANSMIT command. Furthermore, if you overwrite the TBPTR or execute the INIT
TX PARAMETERS command, the STOP TRANSMIT command is not required.
2. Clear the ENT bit in the GSMR_L. The SCC2 transmitter is now disabled and put in a
reset state.
3. Make modifications to the SCC2 transmit parameters or to the parameter RAM. If you
want to switch protocols or restore the SCC2 transmit parameters to their initial state,
issue the INIT TX PARAMETERS command to the CPCR.
4. Issue the RESTART TRANSMIT command to the CPCR. This command is required if
the INIT TX PARAMETERS command was not issued in step 3.
5. Set the ENT bit in the GSMR_L. Transmission begins using the TX buffer descriptor
that the TBPTR points to as soon as the R bit is set in the TX buffer descriptor.
16.9.14.2 DISABLING PART OF THE SCC2 TRANSMITTER. To reinitialize the SCC2
transmitter to the state it was in after reset, follow this short sequence of steps:
1. Clear the ENT bit in the GSMR_L.
2. Issue the INIT TX PARAMETERS command and make any additional modifications.
3. Set the ENT bit in the GSMR_L.
Note: Modifying parameter RAM does not require that you fully disable the serial
communication controller. Refer to the parameter RAM description for details on
when parameter RAM values can be modified. If you prefer to disable the USB,
SCC2, SMCs, SPI, and the I2C, use the CPCR to reset the entire communication
processor module with a single command.