Motorola MPC8260 User Manual

21-16

MOTOROLA

19. Initialize the TxBD. Assume the Tx data frame is at 0x0000_2000 in main memory 

and contains Þve 8-bit characters. TxBD[Status and Control] = 0xBC00, 
TxBD[Data Length] = 0x0005, and TxBD[Buffer Pointer] = 0x0000_2000.

20. Write 0xFFFF to SCCE to clear any previous events.

21. Write 0x001A to SCCM to enable TXE, RXF, and TXB interrupts.

22. Write 0x0040_0000 to the SIU interrupt mask register low (SIMR_L) so the SMC1 

can generate a system interrupt. Initialize SIU interrupt pending register low 
(SIPNR_L) by writing 0xFFFF_FFFF to it.

23. Write 0x0000_0000 to GSMR_H2 to enable normal CTS and CD behavior with 

idles (not ßags) between frames.

24. Write 0x0000_0000 to GSMR_L2 to conÞgure CTS and CD to control transmission 

and reception in HDLC mode. Normal Tx clock operation is used. Notice that the 
transmitter (ENT) and receiver (ENR) have not been enabled. If inverted HDLC 
operation is preferred, set RINV and TINV.

25. Write 0x0000 to PSMR2 to conÞgure one opening and one closing ßag, 16-bit 

CCITT-CRC, and prevent multiple frames in the FIFO.

26. Write 0x00000030 to GSMR_L2 to enable the SCC2 transmitter and receiver. This 

additional write ensures that ENT and ENR are enabled last.

Note that after 5 bytes and CRC have been sent, the Tx buffer is closed; the Rx buffer is
closed after a frame is received. Frames larger than 256 bytes cause a busy (out-of-buffers)
condition because only one RxBD is prepared.

The following sequence initializes an HDLC channel that uses the DPLL in a Manchester
encoding. Provide a clock which is 16

´ the chosen bit rate of CLK3. Then connect CLK3

to the HDLC transmitter and receiver. (A baud rate generator could be used instead.)
ConÞgure SCC2 to use RTS2, CTS2, and CD2.

1. Follow steps 1Ð22 in example #1 above.

2. Write 0x004A_A400 to GSMR_L2 to make carrier sense always active, a 16-bit 

preamble of Ô01Õ patterns, 16

´ operation of the DPLL and Manchester encoding for 

the receiver and transmitter, and HDLC mode. CTS and CD should be conÞgured to 
control transmission and reception. Do not set GSMR[ENT, ENR].

3. Write 0x0000 to PSMR2 to use one opening and one closing ßag and 16-bit CCITT-

CRC and to reject multiple frames in the FIFO.

4. Write 0x004A_A430 to GSMR_L2 to enable the SCC2 transmitter and receiver. 

This additional write to GSMR_L2 ensures that ENT and ENR are enabled last.