Although I have started my own site (http://www.undergroundcm.com)with my own forums (http://www.undergroundcm.com/forum/index.php), I wanted to post this in the GamesX forums exclusively before posting it in my own. This site inspired me to become active in the console modding scene and I have come a long way since my days of lurking around these forums soaking up information. But anyways enough about this, on with the show!
The TG-16/PCE is an extremely capable system with a marginally fast CPU. There are a lot of games that can overwork the CPU and create slowdown or "lag" which can cause games to appear to run in slow motion. overclocking the CPU helps the CPU maintain a steady 60 frames-per-second without the graphics chip having to output the same frame twice.
If any of you have ever played Air Zonk on the TG-16/PCEngine, you know how slow the game can run, and understandably so. Air Zonk is my favorite game for the platform, and the slowdown began to really get to me, so I began to investigate.
Honestly, this was the easiest overclock I have ever performed, and the TG-16/PCE really shines with a faster CPU.
______________________________________________________The ProcedureThe Subject:
an unsuspecting PCEngine Core Grafix
The TG-16/PCE contains a custom CPU designed by Hudson and is based on a 6502 core. The biggest modification is the addition of a 6-channel PSG audio synthesizer that shares the same frequency as the CPU itself. With this information in mind, I knew that the audio would be affected most likely with a pitch increase.
looking at the motherboard, there are 3 chips that are all identical in size and packaging:HuC6280A = CPU. Operates at 7.19 MHz (3.58 in some rare cases)
HuC6270A = VDP. essentially the GPU
HuC6260A = Video Encoder
The 6280 is the CPU and the chip we will be dealing with. The CPU recieves a clock signal of 21.477 MHz directly from an oscillator on the motherboard. The CPU divides any signal it recieves by 3 and the product is the CPU's operational speed. This oscillator is for the CPU only, and does not affect any other components...yay!
The clock input pin on the CPU is pin #15, this is where the CPU recieves the 21.477 MHz stock signal. All we need to do is disconnect it from this signal and give the CPU a signal of our own via a 4-pin crystal oscillator (http://en.wikipedia.org/wiki/Crystal_oscillator). In this case, I am going to use a 25 MHz crystal oscillator. This, in theory, should give me a CPU speed of 8.3 MHz. Not a super high increase, but it should be enough to smooth out those games without affecting the audio too much. Your 4-pin oscillator should be wired in this fashion: (Note the dot on one of the corners of the oscillator, this does not connect to anything)
The easiest way to disconnect the original signal from the CPU is to *CAREFULLY* lift pin #15 off of the motherboard. Do this at your own risk, and very carefully, as these pins are fragile!!!!
If you have your oscillator wired, all you need to do is connect your clock output to pin #15 on your CPU. And your done! Double check, assemble, and test.
With my 4 MB TG16/PCE flash card in hand, I was ready to test all types of games... I think I tested over 100 from different regions. All games had a slightly higher-pitched audio as expected, but i don't mind it. Here are some game behaviors worth noting:
Air Zonk - Ran *drastically* faster... still some slowdown though.
Magical Chase - Runs great. Shopping for items makes the screen flicker a bit.
Victory Run - Scaled road breaks up a bit.
I am very interested in hearing your personal experiences with overcocking this system. I wish I had pictures to go along with this article, but I sold the PCE and flash card when I was offered a price I couldn't pass up. Good Luck!!
That's pretty fascinating.
How does it affect peripherals, like the CD ROM?
Actually thats where I would need the help of the UCM and GamesX communities to test. I don't have a CD-ROM attachment or access to a Turbo-Duo.
I had a flash card, so essentially I could test any game I wanted; but I didn't test R-Type.
Music is faster/higher pitched simply because most games use a timer to sync the music in game. The speed of that timer is linked to the cpu speed.