Directed Electronics 3200HS Informações Técnicas descarregar pdf (Página 17)

SCI to SPI Peripheral Communication in V850ES Microcontrollers

Figure 8. MCU Connections to DS1722 Temperature Sensor

SDI

SCLK

SDO

DS1722

SERMODE

µC

The polarity of the serial clock depends on its state when CE is asserted. Assuming SCLK is low when

CE goes high, the idle state of SCLK is low, which is equivalent to CPOL=0. If SCLK is high when CE

goes high, the idle state of SCLK is high, which is equivalent to CPOL=1.

For compatibility with the MAX6627, we will assume SCLK is low when idle (CPOL=0), and the first

edge of SCLK will be a rising edge. The interface to master unit uses the first edge of the serial clock as

the data drive strobe (when driving data to the master) and the trailing edge of serial clock as the data

capture strobe (when accepting data from the master). For an SPI controller, this would require CPHA=1,

which is equivalent to an NEC Electronics CSI type 3 interface.

NEC Electronics CSI clocking type CKPn = 1 DAPn = 0 Type 3 interface

SPI clocking method CPOL = 0 CPHA = 1

After CE is activated, the DS1722 sensor expects the master to transmit an address by sending eight bits

of data to SDI; during these eight bits, the SDO output will be in the high-impedance state, and the

DS1722 will clock in eight bits of address on the trailing edges of SCLK. Depending on the address, the

DS1722 will then drive SDO, ignoring further input on SDI (read operation from DS1722), or will

continue to read data on SDI and keep SDO in the high-impedance state (write operation to DS1722).

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