SH79F6488PSLASH080PR datasheet(84/152 Pages) SINOWEALTH

84 / 152 page

SH79F6488/SH79F6489

Slave Mode

(1) Enable

The SPI operates in slave mode when the MSTR is cleared in the SPCON register. Before a data transmission occurs, the

slave select (SS

———

) pin of the Slave device must be set to ’0’. The SS

———

pin must remain low until the 1-byte transmission is

complete.

(2) Transmit & Receive

When in SPI slave mode, bytes are shifted in through the MOSI pin and out through the MISO pin by a master device

controlling the SCK signal. A bit counter counts SCK edges. When 8 bits have been shifted in the receive shift register and

another 8 bits have been shifted out the transmit shift register, the SPIF flag is set to logic ‘1’. Data is read from the receive

shift register by reading SPDAT. If interrupts are enabled, an interrupt request is generated when the SPIF flag is set.

To prevent an overflow condition, the SPI slave software must clear the SPIF bit in SPSTA register before another byte

enters the receive shift register. Else a RXOV signal will be set to indicate data over-run occurs, and the receive shift register

keep the byte that SPIF was lastly set, also the SPI slave will not receive any further data until SPIF was cleared.

A SPI slave cannot initiate transfers. Data to be transferred to the master device is pre-loaded into the shift register by

writing to SPDAT. Writes to SPDAT are placed in the transmit buffer first. So a SPI slave must complete the write to the

SPDAT (transmit shift register) in one SPI clock before the master starts a new transmission. If the write to SPDAT is late in

the first transmission, the SPI slave will transmit a ‘0x00’ byte in the following transmission. if the write operation occurs

during this time, a WCOL signal will be set. If the transmit shift register already contains data, the SPI slave will generate a

WCOL signal to indicate writing too fast. But the data in transmit shift register will not be affected, and the transmission

continues uninterrupted.

SH79F6488P/080PR Datasheet(PDF) 84 Page - SINOWEALTH Electronic Ltd