MEC1322 datasheet(316/456 Pages) MICROCHIP

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MEC1322

DS00001719D-page 316

 2014 - 2015 Microchip Technology Inc.

The phase of the clock is selected independently for receiving data and transmitting data. The receive phase is deter-

mine by RCLKPH and the transmit phase is determine by TCLKPH in the SPI Clock Control Register.

The following table summarizes the effect of CLKPOL, RCLKPH and TCLKPH.

27.11 SPI Examples

27.11.1

FULL DUPLEX MODE TRANSFER EXAMPLES

27.11.1.1

Read Only

The slave device used in this example is a MAXIM MAX1080 10 bit, 8 channel ADC:

• The SPI block is activated by setting the enable bit in SPIAR - SPI Enable Register

• The SPIMODE bit is de-asserted '0' to enable the SPI interface in Full Duplex mode.

• The CLKPOL and TCLKPH bits are de-asserted '0', and RCLKPH is asserted '1' to match the clocking require-

ments of the slave device.

• The LSBF bit is de-asserted '0' to indicate that the slave expects data in MSB-first order.

• Assert CS# using a GPIO pin.

• Write a valid command word (as specified by the slave device) to the SPITD - SPI TX_Data Register with TXFE

asserted '1'. The SPI master automatically clears the TXFE bit indicating the byte has been put in the TX buffer. If

the shift register is empty the TX_DATA byte is loaded into the shift register and the SPI master reasserts the

TXFE bit. Once the data is in the shift register the SPI master begins shifting the data value onto the SPDOUT pin

and drives the SPCLK pin. Data on the SPDIN pin is also sampled on each clock.

• Once the TXFE bit is asserted the SPI Master is ready to receive its next byte. Before writing the next TX_DATA

value, software must clear the RXBF status bit by reading the SPIRD - SPI RX_Data Register.

TABLE 27-8:

SPI DATA AND CLOCK BEHAVIOR

CLKPOL

RCLKPH

TCLKPH

Behavior

Inactive state is low. First edge is rising edge.

Data is sampled on the rising edge.

Data is transmitted on the falling edge.

Data is valid before the first rising edge.

Inactive state is low. First edge is rising edge.

Data is sampled on the rising edge.

Data is transmitted on the rising edge.

Inactive state is low. First edge is rising edge.

Data is sampled on the falling edge.

Data is transmitted on the falling edge.

Data is valid before the first rising edge.

Inactive state is low. First edge is rising edge.

Data is sampled on the falling edge.

Data is transmitted on the rising edge.

Inactive state is high. First edge is falling edge.

Data is sampled on the falling edge.

Data is transmitted on the rising edge.

Data is valid before the first falling edge.

Inactive state is high. First edge is falling edge.

Data is sampled on the falling edge.

Data is transmitted on the falling edge.

Inactive state is high. First edge is falling edge.

Data is sampled on the rising edge.

Data is transmitted on the rising edge.

Data is valid before the first falling edge.

Inactive state is high. First edge is falling edge.

Data is sampled on the rising edge.

Data is transmitted on the falling edge.

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