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Introduction
Variable Speed DC Fan Control using the MC9RS08KA2, Rev. 0
8 Freescale Semiconductor
1.2 Freescale’s New Generation Ultra Low Cost MCU
The MC9RS08KA2 microcontroller unit (MCU) is an extremely low cost, small pin count device for home
appliances, toys, and small geometry applications, such as a DC fan controller. This device is composed
of standard on-chip modules including a very small and highly efficient RS08 CPU core, 62 bytes RAM,
2K bytes FLASH, an 8-bit modulo timer, keyboard interrupt, and analog comparator. The device is
available in small 6- and 8-pin packages.
Features of the MC9RS08KA2 include:
• 8-bit RS08 core
– Up to 10 MHz (bus frequency) at 1.8V for 100 ns minimum instruction time
– RS08 instruction set
– Supports tiny/short address mode
– 14-byte fast-access RAM
– Allows emulation of HC08/HCS08 zero-offset index addressing mode instructions
• Third-generation Flash and RAM (extremely fast, byte writable programming)
– 63 Byte RAM
– 2K Byte Flash
• Flexible clock options
• 4 Bidirectional I/O lines with software selectable pull-up (eliminates need for external resistors)
• Analog comparator
• Real time interrupt
• 8-bit timer with 8-bit prescale
• System protection
– Resets in instance of runaways or corrupted code
– Low voltage detection
– Illegal opcode and illegal address detection
– Flash security feature
• Single wire debugging and emulation interface; eliminates need for expensive emulation tools or
development hardware
1.3 DC Fan Reference Design Targets
Table 1-1. Design Targets
Item Requirement
Motor Type Bi-phase BLDC motor
Fan Dimensions 60mm x 60mm x 25mm
Operating Voltage 12V
Current Rating 0.18A (max.)
Speed 1000 to 4000 RPM
Temperature Feedback Yes
Fault Detection Air flow blocking (motor jam)
Fault Notification Buzzer alarm