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CSI to SPI Peripheral Communication in V850ES Microcontrollers

The twelve bits of temperature data is in degrees centigrade, with the upper eight bits (D14 to D7)

indicating degrees, and the lower four bits (D6 to D3) indicating sixteenths of a degree. If the lower

three bits are masked to zero, the 16-bit signed value can be taken as (temperature in ºC) × 128.

Table 3. Examples of Binary, Hexadecimal, and Degree Representations of Temperature Data

Binary Temperature Data Hexadecimal Temperature Data Temperature (ºC)

0100 1000 1000 0000 4880H 145

0011 1100 0000 0000 3C00H 120

0011 0010 0000 0000 3200H 100

0001 1011 1000 0000 1B80H 55

0000 1010 0000 0000 0A00H 20

0000 0000 1000 0000 0080H 1

0000 0000 0000 1000 0008H 0.0625 (1/16)

0000 0000 0000 0000 0000H 0

1111 1111 1111 1000 FFF8H –0.0625 (–1/16)

1111 1111 1000 0000 FF80H –1

1111 0110 0000 0000 F600H –20

1110 0100 1000 0000 E480H –55

In this format, the maximum positive temperature value would be 7FF8H (0111 1111 1111 1000

binary), equivalent to +255.9375ºC. The maximum negative temperature value would be 8000H

(1000 0000 0000 0000 binary), equivalent to –256ºC. The device itself will not operate at these

extremes, and data from the remote sensor is only interpreted from –5 to +145ºC.

2.4.2 Dallas Semiconductor DS1722

The DS1722 is a temperature sensor device with a built-in SPI-compatible serial interface. This

read/write slave device has no remote transistor for temperature sensing; the temperature of the

device itself is read. A configuration register can be written, and the temperature high and low

bytes and configuration register can be read. The serial clock (SCLK) input is driven by the master

unit’s SCK signal; the serial data output (SDO) would be connected to the serial input (SI) of the

master unit, and the serial data input (SDI) is connected to the serial output (SO) of the master unit.

The DS1722 can do temperature conversions continuously, or one at a time, and then enter a

power-down mode (one-shot conversion). The conversion mode is controlled by a bit in the

configuration register. The latest temperature conversion is available for reading at any time.

The serial mode (SERMODE) and chip enable (CE) pins control communication. The SERMODE

pin selects the communication method; when high, SERMODE selects SPI mode. When CE is

high, the DS1722 temperature is enabled for communication and will respond to SCLK by reading

SDI and driving SDO; when CE is low, the DS1722 temperature sensor will ignore activity on the

SCLK, SDI, and SDO pins.

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