
MOTOROLA
Appendix C. TPU3 ROM Functions
C-49
Serial Input/Output Port (SIOP)
C.19.1.1 CHAN_CONTROL
This 9-bit, CPU-written parameter is used to set up the clock polarity for the SIOP data
transfer. The valid values for CHAN_CONTROL for this function are given in the table
below. CHAN_CONTROL must be written by the host before issuing the host service
request (HSR) to initialize the function.
C.19.1.2 BIT_D
BIT_D is a CPU-written bit that determines the direction of shift of the SIOP data. If BIT_D
is zero, then SIOP_DATA is right shifted (LSB first). If BIT_D is one then SIOP_DATA is
left shifted (MSB first).
C.19.1.3 HALF_PERIOD
This CPU-written parameter defines the baud rate of the SIOP function. The value
contained in HALF_PERIOD is the number of TCR1 counts for a half-SIOP clock period
(for example, for a 50 baud rate, with a TCR1 period of 240 ns, the value [(1/50)/2]/240 ns
= 42) should be written to HALF_PERIOD. The range for HALF_PERIOD is 1 to 0x8000,
although the minimum value in practice will be limited by other system conditions. See the
the SIOP function.
C.19.1.4 BIT_COUNT
The TPU3 uses this parameter to count down the number of bits remaining during a transfer
in progress. During the SIOP initialization state, BIT_COUNT is loaded with the value
contained in XFER_SIZE and then decremented as the data is transferred. When it reaches
zero, the transfer is complete and the TPU3 issues an interrupt request to the CPU.
C.19.1.5 XFER_SIZE
This CPU-written parameter determines the number of bits that make up a data transfer.
During initialization, XFER_SIZE is copied into BIT_COUNT. XFER_SIZE is shown as
a 5-bit parameter to match the maximum size of 16 bits in SIOP_DATA, although the TPU3
uses the whole word location. For normal use, XFER_SIZE should be in the 1- to 16-bit
range.
Table C-30. SIOP Function Valid CHAN_Control Options
CHAN_CONTROL 1
8 7 6 543 21 0
1 Other values of CHAN_CONTROL may result in indeterminate operation.
Resulting Action
0 1 0 0 0 1 1 0 1
Data valid on clock Falling edge.
01 00 01 11 0
Datavalid on clock Risingedge.