Re: Processor Upgrade?
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Re: Processor Upgrade?
John Bernatz wrote in message <35CF5BB9.7A63@geocities.com>...
>I get an electronic parts catalog and saw a Zilog Z80 8mhz processor and
>was wondering if it would be possible to replace the processor in any ti
>calc with a Zilog Z80 6mhz.
There are two reasons why it wouldn't work.
1) The processor in the calculator is NOT a Zilog Z-80. It's a CMOS
version of a Z-80 COMPATIBLE processor. It's surface mounted, not a 40-pin
DIP like the true Z-80.
2) Even if you could mount it, the clock speed wouldn't go up. The 8Mhz
rating of the Z-80 is it's maximum guaranteed speed, NOT how fast it
actually runs in a circuit. The actual speed is controlled in either of two
ways. First, in true computers, a crystal is used to provide a steady
frequency. This is rather expensive for a calculator and such an accurate
clock signal isn't needed so TI chose a less expensive way. This is a
Resistor-Capacitor (R/C) network.
Various values of resistor and capacitor are used and the frequency is
determined by the discharge of the capacitor which is controlled by the
amount of resistance. This is why the famous calc speed-up works. All you
have to do is change the value of the resistor (or eliminate it altogether)
and the R-C network will run the calculator up to three times faster. This
way you get up to an 18Mhz calc without adding extra hardware. Some people
wire a switch in so they can switch back and forth between the original
clock speed and the "Turbo" mode. This is because some games (especially
machine language games) are too fast in turbo mode.
Tom Lake
References: