Renesas SH7781 - Manual (Page 1168)

22. Serial I/O with FIFO (SIOF)
Rev.1.00 Jan. 10, 2008 Page 1138 of 1658
REJ09B0261-0100
Table 22.12 Conditions to Issue Receive Request
RFWM2 to
RFWM0 Number of
Requested Stages*
Receive Request Used Areas
000 1 Valid data is 1 stage or more
100 4 Valid data is 4 stages or more
101 8 Valid data is 8 stages or more
110 12 Valid data is 12 stages or more
Smallest
111 16 Valid data is 16 stages Largest
Note: * The number of requested stages is the number of stages in transmit/receive FIFO.
The number of stages of the FIFO is always sixteen even if the data area or empty area exceeds the
FIFO size. Accordingly, an overflow error or underflow error occurs if data area or empty area
exceeds sixteen FIFO stages.
The FIFO transmit or receive request is canceled when the above condition is not satisfied even if
the FIFO is not empty or full.
(3) Number of FIFOs
The number of FIFO stages used in transmission and reception is indicated by the following
register.
• Transmit FIFO: The number of empty FIFO stages is indicated by the TFUA4 to TFUA0 bits
in SIFCTR.
• Receive FIFO: The number of valid data stages is indicated by the bits RFUA4 to RFUA0 bits
in SIFCTR.
The above indicates possible data numbers that can be transferred by the CPU or DMAC.