MEC1322 datasheet(319/456 Pages) MICROCHIP

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DS00001719D-page 319

MEC1322

• If no more data needs to be received by the master, CS# is released and the SPI is idle. Otherwise, master contin-

ues reading the data by writing a dummy value to the TX_DATA register after every 8 SPI_CLK cycles.

Write

• 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, TCLKPH and RCLKPH bits are de-asserted '0' to match the clocking requirements of the slave

device.

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

• Assert WR# high using a GPIO pin.

• Assert CS# low 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 SPI_CLK 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.

• Next, EEPROM address A15-A8 is written to the TX_DATA register. The SPI master automatically clears the

TXFE bit, but does not begin shifting the dummy data value onto the SPDOUT pin. This byte will remain in the

TX_DATA register until the TX shift register is empty.

• After 8 SPI_CLK pulses from the first transmit byte (Command Byte transmitted):

- The first SPI cycle is complete, RXBF bit is asserted '1', and the SPINT interrupt is asserted, if enabled. The

data now contained in SPIRD - SPI RX_Data Register is invalid since the last cycle was initiated solely to

transmit command data to the slave. This particular slave device tri-states the SPDIN pin to the master while

it is accepting command data. This SPIRD data is ignored.

USER’S NOTE:

External pull-up or pull-down is required on the SPDIN pin if it is tri-stated by the slave device.

- Once the first SPI cycle is completed, the SPI master takes the pending data in the TX_DATA register

(EEPROM address A15-A8) and loads it into the TX shift register. Loading the shift register automatically

asserts the TXFE bit, begins shifting the dummy data value onto the SPDOUT pin, and drives the SPI_CLK

pin. Data on the SPDIN pin is also sampled on each clock. Note: The particular slave device ignores address

A15-A13.

• 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.

• Next, EEPROM address A7-A0 is written to the TX_DATA register. The SPI master automatically clears the TXFE

bit, but does not begin shifting this data value onto the SPDOUT pin. This byte will remain in the TX_DATA register

until the TX shift register is empty.

• After 8 SPI_CLK pulses from the second transmit byte (Address Byte (MSB) transmitted):

- EEPROM address A15-A8 has been transmitted to the slave completing the second SPI cycle. Once again,

the RXBF bit is asserted '1' and the SPINT interrupt is asserted, if enabled. The data now contained in SPIRD

- SPI RX_Data Register is invalid since the last cycle was initiated solely to transmit address data to the

slave.

- Once the second SPI cycle is completed, the SPI master takes the pending data in the TX_DATA register

(EEPROM address A7-A0) and loads it into the TX shift register. Loading the shift register automatically

asserts the TXFE bit, begins shifting the dummy 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.

• Next, a data byte (D7:D0) is written to the TX_DATA register. The SPI master automatically clears the TXFE bit,

but does not begin shifting this data value onto the SPDOUT pin. This byte will remain in the TX_DATA register

until the TX shift register is empty.

• After 8 SPI_CLK pulses, the third SPI cycle is complete (Address Byte (LSB) transmitted):

- EEPROM address A7-A0 has been transmitted to the slave completing the third SPI cycle. Once again, the

RXBF bit is asserted '1' and the SPINT interrupt is asserted, if enabled. The data now contained in SPIRD -

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