W79E217A Datasheet, PDF (156/207 Pages) Winbond – 8-bit Microcontroller

Preliminary W79E217A Data Sheet
18.3 Functional descriptions
18.3.1 Master mode
The device can configure the SPI to operate as a master or as a slave, through MSTR bit. When the
MSTR bit is set, master mode is selected, when MSTR bit is cleared, slave mode is selected. During
master mode, only master SPI device can initiate transmission. A transmission begins by writing to the
master SPDR register. The bytes begin shifting out on MOSI pin under the control of SPCLK. The
master places data on MOSI line a half-cycle before SPCLK edge that the slave device uses to latch
the data bit. The SS must stay low before data transactions and stay low for the duration of the
transactions.
Figure 18-2: Master Mode Transmission (CPOL = 0, CPHA = 0)
- 156 -
Publication Release Date: December 14, 2007
Revision A3.0