After poking around Cemetech and talking to some of the higher ups, I decided to try my hand at hardware overclocking my Ti 84+.

I've been aware of asm ways to change the clock mode from 8MHz to 16MHz before, but I wanted to try and imitate what others have done by changing resistor values.

My first idea was to change out a resistor and a capacitor like we did in the good ol' days of the Ti 83. Alas, this did not go over well when I opened up the 84+ and barely recognized any piece of hardware.

KermM pointed me in the direction of an overclocking thread in which a few have overclocked the Ti 84+ C SE and such (here: http://cemete.ch/t8936)

After studying Val's post on page 2, I finally found the right R07D resistor (hiding under a blob of glue) and desoldered it. Next I took a 5k trim pot and soldered it to the pads using some REALLY thin wire)

After testing to make sure I didn't destroy the calculator, I set about filing down a nice hole for accessing the pot that I hot-glued to the PCB. I was going for a position in which I wouldn't accidentally bump it but still be able to change the value.

Here is the finished result (I should have taken assembly pictures):


Here's the DrDnar's speed test:


While this works and all, why does the cpu report 5.5278MHz as the base clock and then jump right up to the 22.xxMHz? Does this mean that the calculator is actually running at 5.5278MHz for normal use unless otherwise specified?
Nice! The calculator does not run at exactly 6Mhz or 15Mhz, so yea, your "calculator is actually running at 5.5278MHz for normal use" Wink
Actually, the OS normally runs at 15 MHz. It reverts to 6 MHZ when it calls out to external code, like apps, hooks, and RAM programs, which then have to set 15 MHz again if the programmer wants it. You can tell it normally runs at 15 MHz because graphing---if you disable asymptote detection---is faster than on the TI-83 Plus, as is BASIC program execution.

If you disassemble page 0, you'll see the OS has an internal call to push the current CPU speed onto the stack and set 6 MHz mode, and another one to pop the CPU speed off the stack. If I remember correctly, the TI-84 Plus (C)(SE) OS retains the hardware check for the TI-83 Plus SE (a long discontinued model) before doing that. So yeah, it wastes time doing a useless check.

Good job on the soldering! I never would have attempted that, and my calculator has larger 0204 (I think?) resistors. I think the newer models use smaller 0102 resistors, so that's fine soldering indeed. WikiTI has a page on overclocking, but it doesn't have a picture of the new hardware with the new ASIC. I'm actually a bit surprised that the resistor was still labeled the same, because the ASIC pinout is different. I currently have a new hardware calculator at my disposal, so I guess I should do a PCB photo of it, too.

The CPU clock circuit is sensitive to not just the resistance of those two resistors, but also the capacitance of a small capacitor; the capacitor is integral to the circuit. As far as I know---though I haven't done any kind of mass study on this, so take this with a grain of salt---, the 6 MHz speeds tend to go higher rather than lower. So, I suppose it's possible that you're getting a slower 6 MHz speed because you added extra capacitance to the circuit with your trim pot.

And it's always cool to see somebody using my CPU speed test tool.
*bump*

Is it possible that my calculator (this one with the trim pot) isn't running stable 100% because the capacitance is a little screwed? Should I change the capacitor to something slightly smaller? I could try to find an i2c capacitor if I have to.

Also, this would push the calculator to the 6MHz point, right?
  
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