Microchip Technology DM164123 Data Sheet
PICDEM™ SYSTEM MANAGEMENT
USER’S GUIDE
©
2007 Microchip Technology Inc.
DS41304B-page 15
Chapter 2. Background
2.1
INTRODUCTION
This chapter provides background information on the System Management application
and the PICDEM System Management Board. It also provides background information
on the fan drive circuitry that is available on the board. Additional detailed information
can be found in the PICDEM System Management presentation and source code
included on the CD-ROM.
and the PICDEM System Management Board. It also provides background information
on the fan drive circuitry that is available on the board. Additional detailed information
can be found in the PICDEM System Management presentation and source code
included on the CD-ROM.
2.2
HIGHLIGHTS
Topics covered in this chapter include:
• PICDEM™ System Management Board and PICkit™ Serial Analyzer
• Fan Speed Control
2.3
PICDEM™ SYSTEM MANAGEMENT AND PICKIT™ SERIAL ANALYZER
The PICDEM™ System Management emulates four I
2
C peripherals usually found on
a system management bus. The real-time clock, ADC, serial EEPROM and thermal
management controller peripherals, typically reside on the I
management controller peripherals, typically reside on the I
2
C bus line of rack-mount
servers and motherboards. The PIC16F886 integrates the functions of each device on
the I
the I
2
C communications bus, while responding to the specific address calls for each
device.
The PICkit Serial Analyzer is a utility that allows control and monitoring of the I
2
C bus.
It is able to generate the specific device calls and interpret data. This data can then be
translated to a personal computer and can be interacted with through a graphical user
interface. In the PICDEM™ System Management Board, the PICkit Serial Analyzer
takes the place of the bus master that manages the devices on the I
translated to a personal computer and can be interacted with through a graphical user
interface. In the PICDEM™ System Management Board, the PICkit Serial Analyzer
takes the place of the bus master that manages the devices on the I
2
C bus.
2.4
FAN SPEED CONTROL
2.4.1
Two-wire Fan
Two-wire fans provide power and ground terminals. The fan can be controlled through
low-speed (10-100 Hz) PWM.
low-speed (10-100 Hz) PWM.
As the duty cycle of the PWM signal increases, fan speed increases non-linearly. Fan
speed feedback can be determined by measuring the time between commutation pulse
noise that is generated on each revolution of the fan. Low-speed PWM can be
generated by PIC microcontrollers using the Enhanced Capture/Compare/PWM
module. Speed can be measured with comparator and timer peripherals.
speed feedback can be determined by measuring the time between commutation pulse
noise that is generated on each revolution of the fan. Low-speed PWM can be
generated by PIC microcontrollers using the Enhanced Capture/Compare/PWM
module. Speed can be measured with comparator and timer peripherals.
Note:
Be sure to verify with the fan manufacturer that the fan specifications allow
for PWM control of input voltage.
for PWM control of input voltage.