Motorola MPC823e - Page 653

Communication Processor Module
MOTOROLA MPC823e REFERENCE MANUAL 16-199
SCCs
COMMUNICATION
16
PROCESSOR MODULE
16.9.14 Disabling the SCCs On-the-Fly
If you are not using the serial communication controllers, you can disable them and reenable
them later by following a sequence of steps to ensure that any buffers currently in use are
properly closed and that new data is transferred to or from a new buffer. You must follow this
sequence 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 SCCx TRANSMITTER. The SCCx transmitter can be
fully disabled or enabled by following these steps:
1. Issue the STOP TRANSMIT command to the CPCR if a serial communication
controller is currently transmitting data. It must stop smoothly. If a 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 to disable the SCCx transmitter and put it in a reset
state.
3. Make modifications to the SCCx transmit parameters or to the parameter RAM. If you
want to switch protocols or restore the SCCx 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 SCCx TRANSMITTER. To reinitialize the SCCx
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 controllers. Refer to the parameter RAM description for details
about modifying the parameter RAM values. If you prefer to disable the USB,
SCCs, SMCs, SPI, and I
2
C, use the CPCR (described in Section 16.2.6.1 CPM
Command Register) to reset the entire communication processor module with
a single command.