DM164123 Microchip Technology, DM164123 Datasheet - Page 21

• Manufacturer Part Number: DM164123
• Description: KIT MANAGEMENT SYSTEM PICDEM
• Manufacturer: Microchip Technology
• Series: PICDEM™r
• Type: MCUr

Specifications of DM164123

• Contents: PICDEM™ System Management PCB, PICkit™ Serial Analyzer, 2 CDs, Power Supply and IDE
• Silicon Manufacturer: Microchip
• Core Architecture: PIC
• Core Sub-architecture: PIC16
• Features: MCLR Reset Line And Switch , In-Circuit Serial Programming, I2C Thermal Management Control
• Silicon Core Number: PIC16F
• Silicon Family Name: PIC16F8xxx
• Kit Contents: Board, Serial Analyzer, Batt, Power Supply, CDs, Guides
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• For Use With/related Products: PIC16F886
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Not applicable / Not applicable

Background
2.4.4
Four-wire Fan Control
Four-wire fan control provides a PWM input, tachometer output, fan power and ground.
Instead of switching fan power, which must be done with two and three-wire fans, only
the PWM input line is switched (typically at 10 kHz–30 kHz). As duty cycle of the fan
increases, speed also increases non-linearly. The tachometer line is the same as the
three-wire fan, generating pulses based on the rotation of the permanent magnet of the
fan; however, the Hall sensor is always on. Therefore, PWM stretching is not needed
to ensure an accurate measurement.
© 2007 Microchip Technology Inc.
DS41304B-page 17