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Follow these steps to handle an SCC interrupt:
1. When an interrupt occurs, read SCCE to determine the interrupt sources and clear
those SCCE bits (in most cases).
2. Process the TxBDs to reuse them if SCCE[TX] or SCCE[TXE] = 1. If the transmit
speed is fast or the interrupt delay is long, the SCC may have sent more than one Tx
buffer. Thus, it is important to check more than one TxBD during interrupt handling.
A common practice is to process all TxBDs in the handler until one is found with its
R bit set.
3. Extract data from the RxBD if SCCE[RX], SCCE[RXB], or SCCE[RXF] is set. As
with transmit buffers, if the receive speed is fast or the interrupt delay is long, the
SCC may have received more than one buffer and the handler should check more
than one RxBD. A common practice is to process all RxBDs in the interrupt handler
until one is found with RxBD[E] set.
4. Execute the rÞ instruction.
Additional information about interrupt handling can be found in Section 4.2, ÒInterrupt
Controller.Ó
19.3.4 Initializing the SCCs
The SCCs require that a number of registers and parameters be conÞgured after a power-on
reset. Regardless of the protocol used, follow these steps to initialize SCCs:
1. Write the parallel I/O ports to conÞgure and connect the I/O pins to the SCCs.
2. ConÞgure the parallel I/O registers to enable RTS, CTS, and CD if these signals are
required.
3. If the time-slot assigner (TSA) is used, the serial interface (SIx) must be conÞgured.
If the SCC is used in NMSI mode, CMXSCR must still be initialized.
4. Write all GSMR bits except ENT or ENR.
5. Write the PSMR.
6. Write the DSR.
7. Initialize the required values for this SCCÕs parameter RAM.
8. Initialize the transmit/receive parameters via the CP command register (CPCR).
9. Clear out any current events in SCCE (optional).
10. Write ones to SCCM register to enable interrupts.
11. Set GSMR_L[ENT] and GSMR_L[ENR].
Descriptors can have their R or E bits set at any time. Notice that the CPCR does not need
to be accessed after a hardware reset. An SCC should be disabled and reenabled after any
dynamic change to its parallel I/O ports or serial channel physical interface conÞguration.
A full reset can also be implemented using CPCR[RST].
MOTOROLA
Chapter 19. Serial Communications Controllers (SCCs)
Part IV. Communications Processor Module
19-17
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