Chameleon-AVR Nurve Networks, Chameleon-AVR Datasheet - Page 263

• Manufacturer Part Number: Chameleon-AVR
• Description: MCU, MPU & DSP Development Tools AVR8 & PROPELLER DEV SYSTEM (SBC)
• Manufacturer: Nurve Networks

Specifications of Chameleon-AVR

• Processor To Be Evaluated: AVR 328P
• Data Bus Width: 8 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

© 2009 NURVE NETWORKS LLC “Exploring the Chameleon AVR 8-Bit”
Appendix H – Overclocking the AVR 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 AVR and Propeller can be over clocked 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 internall 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:
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, this 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 AVR328P Microcontroller
The AVR is a little bit different than the Propeller chip, a little more forgiving, plus its already running at 5V. The AVR is
spec’ed to max out at 20 MHz, but we are running a 16MHz xtal for Arduino compatibility. However, if you do not want to
use Arduino mode, or the bootloader, then go ahead and pop in a 20 MHz parallel resonant mode Xtal and you get 4
MIPs for the taking. However, if you want more than you can do it as well. The max overclock of the AVRs is about 35
MHz before they simply fall apart and stop working. I find that 8xNTSC or 28.636636MHz is a nice compromise. I tested
over 1000 units and they all can sustain this speed. The timings on some of the peripherals become tight for example, the
serial I/O and SPI might error more often and the rate of bit errors with the FLASH memory increases, but 28.636 MHz is
a solid overclocking rate.
The chip will get a little hotter, but not much, the interesting thing though is the chip doesn’t stop malfunctioning due to
overheating, but simply that certain parts of the chip can’t go any faster. For example, the internal SRAM/FLASH has
more limits than say the glue logic inside. So even though most of the chip might run at 40 MHz, it doesn’t matter since
the SRAM and FLASH won’t read correctly.
In conclusion, the AVR will go 28.636 MHz no problem without any changes to the Vcc voltage, or heatsinking needed.
263