UPSD3422 datasheet(139/293 Pages) STMICROELECTRONICS

139 / 293 page

uPSD34xx

SPI (synchronous peripheral interface)

139/293

16, 20, all the way up to 252. For example, if SPICLKD contains 0x24, SPICLK has the

frequency of PERIH_CLK divided by 36 decimal.

The SPICLK frequency must be set low enough to allow the MCU time to read received data

bytes without loosing data. This is dependent upon many things, including the crystal

frequency of the MCU and the efficiency of the SPI firmware.

24.6

Dynamic control

At runtime, bits in registers SPICON0, SPICON1, and SPISTAT are managed by firmware

for dynamic control over the SPI interface. The bits Transmitter Enable (TE) and Receiver

Enable (RE) when set will allow transmitting and receiving respectively. If TE is disabled,

both transmitting and receiving are disabled because SPICLK is driven to constant output

logic ‘0’ (when SPO = 0) or logic '1' (when SPO = 1).

When the SSEL Bit is set, the SPISEL pin will drive to logic '0' (active) to select a connected

slave device at the appropriate time before the first data bit of a byte is transmitted, and

SPISEL will automatically return to logic '1' (inactive) after transmitting the eight bit of data,

as shown in Figure 47 on page 137. SPISEL will continue to automatically toggle this way

for each byte data transmission while the SSEL bit is set by firmware. When the SSEL Bit is

cleared, the SPISEL pin will drive to constant logic '1' and stay that way (after a transmission

in progress completes).

The Interrupt Enable Bits (TEIE, RORIE,TIE, and RIE) when set, will allow an SPI interrupt

to be generated to the MCU upon the occurrence of the condition enabled by these bits.

Firmware must read the four corresponding flags in the SPISTAT register to determine the

specific cause of interrupt. These flags are automatically cleared when firmware reads the

SPISTAT register.

UPSD3422 Datasheet(PDF) 139 Page - STMicroelectronics