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PostPosted: Sun Oct 20, 2002 12:33 am 
Basically, the low voltage dropout regulators are designed into two types.

One is done by straight forward 5 connections to the vid pins, and will cover the entire 1.25 to 3.5 volts for core voltage automatically. The, they have a voltage offset such as 0.9 volts addition to satisfy the resistance of the the length of the traces to the cpu from the mosfet bypass transistor. If you notice some pins not connected, then you do not have all the voltages for your cpu. You might be able to connect those IC pins to the cpu socket where the vid pins are located.

The other regulators have fewer pins, because they designed with seriasl port input in mind. And the core voltage is done by sending the registry information from the bios. You don't know if the core voltage is available or not, until you can set it in the bios. So, the only safe way is to update your bios and see if your cpu of choice will work. Some times you are lucky, that the manufacturer will note the fix they did when they updated the bios. So, you are safe as far as that cpu is concerned. Otherwise, you may have to wait until someone like Unicore can sell you a new bios upgrade to do the core voltage in the bios, unless you can alter the bios yourself?

This generalization on the core voltage regulators, is to prepare you for the compatibility of cpus and motherboards. At least you will not go out on a limb and buy cpus that will not work on your motherboard.

Visual inspection of your motherboard is everything. Look for your core voltage regulator and seearch the internet to identify it and then get your fast cpu.

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PostPosted: Fri Dec 06, 2002 4:37 am 
Often, you don't know whether your motherboard can handle the core voltage of the cpu of your choice. And motherboard manufacturers do not tell you their circuits. You could search the specification and the application circuit of the low drop out voltage regulatore on the internet and see what type of regulator you have.

There are two types of regulators. The earlier ones go directly to the vid pinouts. And there are 5 vid pinouts. If only 3 pins are connected at the regulator, your voltage is limited from 3.5 volts to 2.07 volts. If 4 pins are connected then it will go down to 1.5 volts. If all five pins are connected to the Slot1 or cpu socket then you can go down to 1.2 volts. The vid pinouts to voltage chart was provided by Intel. Some of the earliest motherboards such as the Diamond Micronics C300 with 440LX chipset can handle down to 1.2 volts. In addition, if you are desperate, you can wire the two unconnected regulator pins to the cpu socket with wrap around wires(thin single strand insolated wire) by soldering to the right locations on the cpu socket.

Later, the low drop out voltage regulators have less pins on the IC, because the designers decided to use software to control the core voltage. Software can be send in via serial port, so instead of 5 pins to control the voltage, now you need only two pins. If you have the latest bios verson, you should be able to get down to `1.5 volts or if you are lucky with a 4 mb rom, you can go down to 1.2 volts for your cpu core.

This experience, of course, tells you how to identify your low drop out voltage regulators. Look at the pins which are not connected if your regulator has many pinouts. You should still look for a bios update to see if the updated bios give you more core voltage choices, before you do the extra rewiring to the cpu socket. And if your regulator does not have many pins, to look for the latest bios for you motherboard.

Good luck on your upgrade of your cpu on your motherboard. This helps you to indentify the limit of your motherboard for cpu upgrades.

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PostPosted: Tue Apr 29, 2003 8:53 pm 
Many slot 1 motherboards are built for Intel ppga cpus, however, the chipset might be 66 mhz limited; the core voltage may be quite suitable for fcpga cpus.

Most low drop out voltage regulators have vid0-4 inputs to control the core voltages. Intel had published the vid0-4/core voltage charts, if you are interested. You can search the net. On the other hand, AMD had published the K6-2 power supply design using all the voltage regulators available in the indutry. You can also search on the net and get a copy of it.

What most people don't understand is that vid3 is the range selector. Grounded it runs the upper range of core voltage 2.8 to 3.5v open it runs the 2.0 to 2.8 volts with the vid4 grounded. The vid4 pin controls the 2.0 to 3.5 volts, or opened, it controls the 1.2 volts to 2.0 voltsWhile vid3 closed to ground can control 1.70 to 2.0 volts..

Most voltage regulators which did not provide the correct voltage range can, by using a sharp knife saw off the vid3 or vid4 pins connected to the pcboard to ground and get the core voltage of the lower range for fcpga or even fcpga2 cpus(several I/Opins need capacitance input from the cpu socket).

It is that simple and easy.

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