
C-50
MPC565/MPC566 Reference Manual
MOTOROLA
Serial Input/Output Port (SIOP)
C.19.1.6 SIOP_DATA
This parameter is the data register for all SIOP transfers. Data is shifted out of one end of
SIOP_DATA and shifted in at the other end, the shift direction being determined by the
value of BIT_D. In output-only mode, zero will be shifted into SIOP_DATA and in
input-only mode, the data shifted out is ignored. In clock-only mode, SIOP_DATA is still
shifted.
NOTE
The TPU3 does not “justify” the data position in SIOP_DATA
(for example, if an 8-bit bidirectional transfer is made, shifting
LSB first, then the bottom byte of SIOP_DATA will be shifted
out and the input data will be shifted into the upper byte of
SIOP_DATA).
NOTE
SIOP_DATA is not buffered. The CPU should only access it
between completion of one transfer and the start of the next.
C.19.2 Host CPU Initialization of the SIOP Function
The CPU initializes the SIOP function by:
1. Disabling the channel by clearing the two channel-priority bits
2. Selecting the SIOP function on the channel by writing the assigned SIOP function
number to the function-select bits
3. Writing CHAN_CONTROL in the clock channel parameter RAM
4. Writing HALF_PERIOD, BIT_D, and XFER_SIZE in the clock-channel parameter
RAM to determine the speed, shift direction, and size of the transfer
5. Writing SIOP_DATA if the data output is to be used
6. Selecting the required operating mode via the two host-sequence bits
7. Issuing a host service request type 0b11
8. Enabling service by assigning H, M, or L priority to the clock channel via the two
channel-priority bits
The TPU3 then starts the data transfer, and issues an interrupt request when the transfer is
complete.
Once the function has been initialized, the CPU only needs to write SIOP_DATA with the
new data and issue a HSR 0b11 to initiate a new transfer. In input-only or clock-only modes,
just the HSR 0b11 is required.