CPU Temperature. Lippert Cool FrontRunner PC/104-Plus

Technical Manual “Cool FrontRunner” Version 2.7 17.06.2008 Page 33 of 43

5.5.2 CPU Temperature

The value of the CPU temperature sensor is 9 bits wide. Hence, to read it, the LPC Interface's

Index/Data ports 295h/296h must be used to form a two-part access. Select bank 01 writing ‘01’ to the bank select register at 4Eh. Then read the bits 1…8 from register 50h and take the most significant bit of register 51h as bit 0 to form the complete 9-bit value. Please refer to the following table for calculating temperature.

Debug example: -o 295 4E

-i Æ These are Bits 8..1 of the 9 Bit value. E.g. 22h Æ 0010,0010

-i Æ Take the MSB of this byte as Bit 0

(e.g. value is 00h Æ MSB = 0)

Now the complete 9-bit value would be 0 0100 0100 Æ 044h. As it can be seen from the table below, the temperature value is the decimal register value, divided by 2. Hence:

044h = 68

Temp = 68 / 2 °C = 34°C

Temperature

+125°C

+25°C

+1°C

+0.5°C

0°C

-0.5°C

-1°C

-25°C

-55°C

Board Temperature

8-Bit Binary 8-Bit Hex

0111 1101

0001 1001

7Dh

19h

0000 0001

-

0000 0000

01h

-

00h

-

1111 1111

1110 0111

1100 1001

-

FFh

E7h

C9h

CPU Temperature

9-Bit Binary

0 1111 1010

0 0011 0010

0 0000 0010

0 0000 0001

0 0000 0000

1 1111 1111

1 1111 1110

1 1100 1110

1 1001 0010

9-Bit Hex

0FAh

032h

002h

001h

000h

1FFh

1FEh

1CEh

192h

5.5.3 Fan Speed and PWM regulation

If the Cool FrontRunner is configured to use a 5V system fan (available as an option), it is possible to read out the fan's speed by reading register 28h of the LPC Interface Index/Data Ports

295h/296h.

Debug example: -o 295 28

You can calculate the RPM value with the following equation:

RPM

=

1 .

35

Count

•

•

10

6

Divisor

While the count is the value from above, the divisor consists of Bit 5 in register 5Dh in Bank 0 (Bit 2 of divisor) and register 47h, Bits 5 and 4 (Bit 1 and 0 of divisor). Reading out the Bits values is done as shown in the example above. The default divisor is 2. Changes might be made to get the correct speed, depending on the fan used.

Bit 2 Bit 1 Bit 0 Divisor

0 0 0 1

Technical Manual “Cool FrontRunner” Version 2.7 17.06.2008 Page 34 of 43

0 0 1 2

0 1 0 4

0 1 1 8

1 0 0 16

1 0 1 32

1 1 0 64

1 1 1 128

The default duty cycle of the fan is 100% (FFh). It is possible to reduce the fans speed by setting the duty cycle to lower values. Therefore, you have to write the value to register 5Ah in Bank 0

(remember: Bank Select register Æ 4Eh). 00h Æ 0% = Off, FFh Æ 100% = Full Speed.

Debug example: -o 295 4E

-o 296 80 sets duty cycle to 50%.