Technical information

CSI to SPI Peripheral Communication in V850ES Microcontrollers

the rxbuf[0] location. The first received data will not have been driven by the DS1722, so this first

receive byte does not contain temperature data.

While the dummy data in txbuf[1] is transmitted, the DS1722 will drive the Temperature low byte

out on its SDO pin, and this data will be clocked in on SI00.

After the second byte has been sent, INTCSI00 will occur, and MD_INTCSI00() will transmit

txbuf[2] and read the received temperature low byte into rxbuf[1]. While the dummy data in

txbuf[2] is transmitted, the DS1722 will have advanced its address to 02H, and will drive the

Temperature high byte data out on SDO.

After the third and final byte has been sent, INTCSI00 will occur again, and MD_INTCSI00() will

set the CSI00_SendDone flag, store the last received byte of data (temperature high byte) into

rxbuf[2].

At this point, Temp_Read_2() will see the flag as true, and set the temperature sensor chip select

off, to have the sensor resume temperature readings. It then combines the bytes in rxbuf[1] (first

eight bits from DS1722 = Temperature low byte), and rxbuf[2] (second eight bits from DS1722 =

Temperature high byte) into a signed 16-bit value. In the 10-bit data resolution selected for the

DS1722, this will be (temperature in ºC) × 256, to the nearest 1/4

degree.

To return a temperature value in the same scale as Temp_Read_1(), Temp_Read_2() divides the

signed 16-bit data by two, resulting in (temperature in ºC) × 128, and returns this value.

2.6.12 Temp_Display(temp): Show Temperature in LED

The Temp_Display() routine displays the temperature data in the two-digit LED, by scrolling the

data through the LED digits. The temp parameter is a signed 16-bit value, of temperature × 128.

The routine will display digits in the format of (sign)XXX.YY.

Since the details of this routine have nothing to do with the CSI/SPI interface, the flowchart for this

routine is not shown. A description of the display format follows. For those interested in the

mechanics of the routine, please see the listing in Section 4.

If the temperature is negative, a dash will precede the number for a minus sign, otherwise no sign

will be shown.