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16.7.4.6 SERIAL INTERFACE RAM DYNAMIC CHANGES. The serial interface RAM has
two operating modes:
• A time-division mulitplex channel with a static routing definition. The serial interface
RAM is divided into two parts—transmit (TX) and receive (RX).
• A time-division mulitplex channel that allows dynamic changes. The serial interface
RAM is divided into four parts—two transmits (TX) and two receives (RX).
• Two time-division mulitplex channels with a static routing definition. The serial interface
RAM is divided into four parts—two transmits (TX) and two receives (RX).
• Two time-division mulitplex channels that allows dynamic changes. The serial interface
RAM is divided into eight parts—four transmits (TX) and four receives (RX).
Dynamic changes allow the routing definition of a TDM to be modified while the serial
communication controllers and serial management controllers are connected to it. With fixed
routing, a change has three requirements that must be met before the new routing takes
effect:
• The serial communication controllers and serial management controllers connected to
the time-slot assigner must be disabled.
• The serial interface routing must be modified.
• The serial communication controllers and serial management controllers connected to
the time-slot assigner must be reenabled.
Dynamic changes divide portions of the serial interface RAM into current-route and shadow
RAM. Once the current-route RAM is programmed, the time-slot assigner and serial
interface channels are enabled and time-slot assigner operation begins. When you need to
make a change in routing, you must program the shadow RAM with the new route and set
the CSRRx bit in the serial interface command register to receive and the CSRTx bit to
transmit. As a result, the serial interface exchanges the shadow RAM and the current-route
RAM as soon as the corresponding sync arrives and resets the appropriate CSRxx bit to
signify that the operation has completed. At this time, you can change the routing again.
Notice that the original current-route RAM is now the shadow RAM and vice versa.
Figure 16-51 illustrates an example of the shadow RAM exchange process.
If a TDM with dynamic changes is programmed, the initial current-route RAM addresses in
the serial interface RAM are as follows:
• 0–31 RXA Route
• 64–95 TXA Route
The shadow RAMs are at addresses:
• 32–63 RXA Route
• 96–127 TXA Route
MOTOROLA
MPC823e REFERENCE MANUAL
Communication Processor Module
16-125
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