SH7713 datasheet(675/904 Pages) RENESAS

675 / 904 page

Section 17 Serial I/O with FIFO (SIOF)

Rev.1.50 Aug. 30, 2006 Page 635 of 860

REJ09B0288-0150

17.5

Usage Notes

Note the following when using the SIOF.

1. Using the transmit function in slave mode

If transmission is enabled when data has already been written to the transmit FIFO, one or two

of the first data bytes may be lost.

Therefore, data should not be written to the transmit FIFO before enabling transmission.

2. Using control data transmission/reception consecutively on control data interface (secondary

FS position)

The TCRDY value may become 1 before transmit control data is sent, and if the next control

data is written to the control data register at this point, the control data waiting to be sent will

be overwritten and erased.

At this time, also, the control sequence is disrupted and the SIOF switches around the primary

FS and secondary FS, with the result that transmission/reception of data and control data can

no longer be performed normally.

The control data register should therefore be written to after transmit control data has been

sent.

Example:

Check RCRDY, and write to the control data register when RCRDY is 1.

After transmit control data has been written to, it is essential to read the receive control register

(SIRCR) and clear RCRDY.

3. DMA transfer

Do not use 16-byte DMA transfer. (See section 13.4.4, DMA Transfer Types.)

4. Access from the CPU

When performing access from the CPU, do not access the SIOF's transmit/receive FIFO

consecutively, but instead insert an access to somewhere else between SIOF transmit/receive

FIFO accesses.

5. Transmit/receive FIFO underflow

If the transmit/receive FIFO underflows during a transmit/receive operation, control of the

SIOF's transmit/receive FIFO may fail and data may be lost.

To prevent this, either set a watermark so that an underflow does not occur, or execute a

transmit reset (TXRST) or receive reset (RXRST) when an empty interrupt is generated.

6. Transmit/receive reset execution

When using the SIOF again after a transmit/receive operation ends, or after erroneous

operation occurs, first execute a transmit reset (TXRST) or receive reset (RXRST).

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