SH7721 datasheet(699/1524 Pages) RENESAS

699 / 1524 page

Section 18

Serial Communication Interface with FIFO (SCIF)

Rev. 3.00 Jan. 18, 2008 Page 637 of 1458

REJ09B0033-0300

18.6

Usage Notes

(1)

SCFTDR Writing and the TDFE Flag

The TDFE flag in the serial status register (SCSSR) is set when the number of transmit data bytes

written in the transmit FIFO data register (SCFTDR) has fallen below the transmit trigger number

set by bits TTRG1 and TTRG0 in the FIFO control register (SCFCR). After TDFE is set, transmit

data up to the number of empty bytes in SCFTDR can be written, allowing efficient continuous

transmission.

However, if the number of data bytes written in SCFTDR is less than or equal to the transmit

trigger number, the TDFE flag will be set to 1 again after being cleared to 0. The TDFE flag

should therefore be cleared to 0 after a number of data bytes exceeding the transmit trigger number

has been written to SCFTDR.

The number of transmit data bytes in SCFTDR can be found in the bits 14 to 8 of the FIFO data

count set register (SCFDR).

(2)

SCFRDR Reading and the RDF Flag

The RDF flag in the serial status register (SCSSR) is set when the number of receive data bytes in

the receive FIFO data register (SCFRDR) has become equal to or greater than the receive trigger

number set by bits RTRG1 and RTRG0 in the FIFO control register (SCFCR). After RDF is set,

receive data equivalent to the trigger number can be read from SCFRDR, allowing efficient

continuous reception.

However, if the number of data bytes in SCFRDR exceeds the trigger number, the RDF flag will

be set to 1 again after being cleared to 0. The RDF flag should therefore be cleared to 0 when 1

has been written to RDF after all receive data has been read.

The number of receive data bytes in SCFRDR can be found in the bits 6 to 0 of the FIFO data

count set register (SCFDR).

(3)

Break Detection and Processing

Break signals can be detected by reading the RxD pin directly when a framing error (FER) is

detected. In the break state the input from the RxD pin consists of all 0s, so the FER flag is set and

the parity error flag (PER) may also be set. Note that, although transfer of receive data to

SCFRDR is halted in the break state, the SCIF receiver continues to operate.

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