Chameleon-PIC Nurve Networks, Chameleon-PIC Datasheet - Page 258

• Manufacturer Part Number: Chameleon-PIC
• Description: MCU, MPU & DSP Development Tools PIC24 & PROPELLER DEV SYSTEM (SBC)
• Manufacturer: Nurve Networks

Specifications of Chameleon-PIC

• Processor To Be Evaluated: PIC24
• Data Bus Width: 16 bit
• Interface Type: USB, VGA, PS/2, I2C, ISP, SPI
• Operating Supply Voltage: 3.3 V, 5 V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Appendix H – Overclocking the PIC and Propeller
As with any TTL or CMOS device you can always overclock them. Typically, 10% overclocking will work 99% of the time,
anything higher than 10% you have to take a few things into consideration such as power dissipation, memory response
times, and overall timing of the chips. However, both the PIC and Propeller can be overclocked if you want to get more
performance and are willing to potentially damage the chips.
H.1 Overclocking the Propeller Microcontroller
The Propeller uses an external clock or xtal that is then spun up by an internal PLL. The PLL has a number of power of 2
clock multiplier rates, but typically a 5-10MHz clock (xtal) is used and then the clock multiplier is set at 8x or 16. For
example, the Default2 driver clock directives look like this:
CON
This instructs the compiler to generate an object with settings that assume a 5MHz input clock and then the processor
scales this by 16X resulting in the nominal 80MHz that the Propeller chip needs to operate. The 80 MHz clock drives each
processor clock and each processor executes one instruction per (4) clocks, thus 20 MIPs on average.
Now, if we want to go a little faster, we could use a 6MHZ XTAL and then use the pll16x directive once again, this results
in a clock rate of 96 MHz and 24 MIPS per processor. Depending on your Propeller chip, this might work as is; however,
the transitions are so fast that the noise margins, etc. of the signals become small, and the capacitive loading too much
for the 3.3V supply, thus you might need to increase the power supply voltage to 3.6+ volts to get this speed to work. But,
point is if you need a little bit more, you can increase you oscillator (xtal) a bit and then see if it works.
Also, the Propeller will get hotter as you overclock it, thus you might have to heat sink it.
H.2 Overclocking the PIC24HJ Microcontroller
The PIC is a little bit different than the Propeller chip when overclocking. First of off it is rated to run up to a maximum of
40 MIPS where the internal Fcy clock rate is at 40 MHz. Since the PIC has a divisor and multiplier registers for its PLL we
can run the PLL at different intervals than the Propeller. For example we currently connect to the PIC a 5 MHz xtal and
then use the onboard PLL to multiply that clock rate by 8X for a nominal speed of 40 MHz. However, with our divisor and
multiplier we can take that 5 MHz and clock it at non-integer rates allowing us to achieve ~45 MHz and above. I hesitate
suggesting going above 45 MHz because I have successfully gotten some PIC24s to work at 50 MHz and some did not. It
was just purely device dependent on its max rate. However 45 MHz seemed to work fine for the most part.
The chip will get hotter, but not too much. One thing you can do to dissipate the heat on the PIC chip if it becomes
problematic is to get some silicon sealant and adhere something metal, preferably a heat sink, to the top of the PIC.
In conclusion, the PIC24 will go 45 MHz no problem without any changes to the Vcc voltage, or heatsinking needed.
' These settings are for 5 MHZ XTALS
_clkmode = xtal1 + pll16x
_xinfreq = 5_000_000
' enable external clock and pll times 16
' set frequency to 5 MHZ
© 2009 NURVE NETWORKS LLC “Exploring the Chameleon PIC 16-Bit”
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