MC68F375
TPU ROM FUNCTIONS
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
D-44
D.17.1.1 CHAN_CONTROL
This 9-bit CPU written parameter is used to setup 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 prior to issuing the host service
request (HSR) to initialize the function.
D.17.1.2 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).
D.17.1.3 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 pe-
riod (e.g., for a 50 KHz baud rate, with a TCR1 period of 240 ns, the value [(1/50 KHz)/
2]/240 ns = 42 should be written to HALF_PERIOD. The range for HALF_PERIOD is
1 to $8000, although the minimum value in practice will be limited by other system con-
ditions. See notes on use and performance of SIOP function.
D.17.1.4 BIT_COUNT
This parameter is used by the TPU to count down the number bits remaining while a
transfer is in progress. During the SIOP initialization state, BIT_COUNT is loaded with
the value contained in XFER_SIZE. It is then decremented as the data is transferred
and when it reaches zero, the transfer is complete and the TPU issues an interrupt re-
quest to the CPU.
D.17.1.5 XFER_SIZE
This CPU-written parameter determines the number of bits that make up a data trans-
fer. 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, al-
though the TPU uses the whole word location. For normal use, XFER_SIZE should
be in the range 1-to-16.
D.17.1.6 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
Table D-3 SIOP Function Valid CHAN_Control Options
CHAN_CONTROL1
8 7 6 5 4 3 2 1 0
NOTES:
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.
0 1 0 0 0 1 1 1 0
Data valid on clock Rising edge.
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