VIA Apollo Pro 133/133A Motherboard Roundup - February 2000by Anand Lal Shimpi on February 28, 2000 1:13 AM EST
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Hardware monitoring is one of those often overlooked features of a motherboard. While it's not a necessary component, it can help prevent catastrophic failures or provide valuable information when troubleshooting a problem. For example, you can set an alarm to go off if they system is overheating or a fan has stopped. Some software will even shutdown the system automatically under such circumstances. Many motherboards even throttle back the CPU speed if things start to heat up too much. All this in the name of protecting your system and your data.
One of the beauties of the 686A Super South Bridge is that it features an integrated hardware monitoring solution, meaning that an external chip isn’t necessary. So this section is mainly for the hardware monitoring options that manufacturers can use with the 596B Mobile South Bridge.
Most hardware monitoring chips out there allow for the measurement of system voltages, CPU fan speed, system temperature, and CPU temperature. However, each chip out there has different features when you get into the nitty gritty. Complicating things further is the fact that it is up to each individual motherboard manufacturer to implement those features and every implementation ends up being slightly different. Let's take a look at the different hardware monitoring solutions out there, along with some of the possible implementation issues they may face.
The Winbond 83781D was the first popular hardware monitoring chip on the market. It's actually still used by a few companies that haven't bothered to upgrade to the newer editions of this chip. The 83781D provides monitoring for 5 positive voltages, 2 negative voltages, 3 remote temperatures, and 3 fan speeds. A case open input is also available for added security.
Those 7 voltage inputs are typically used to monitor +/-5V, +/-12V, +3.3V, and Vcore. The remaining voltage input is often used to measure VTT, +5Vsb (standby), Vbat (battery), or the Vcore of a second CPU. The 83781D features five Voltage ID (VID) inputs that read the VID pins of the CPU in order to automatically compensate for different Vcore values from different processors.
The three remote temperatures are read via external thermistors. A thermistor is a device whose resistance varies proportionally to its temperature. These thermistors can be mounted anywhere on the motherboard, but typically at least one is used to monitor the CPU temperature. A CPU thermistor would be mounted either in front of the CPU slot or inside the CPU socket. Some motherboards offer headers that allow you to hook up your own thermistor anywhere in the case. The reaction time and accuracy of the thermistor varies by brand and model.
The 83782D is the success to the 83781D and offers one key advantage - the ability to read CPU temperature from the on-die thermal diode of any 0.25 micron or 0.18 micron Intel CPU. Reading from the on-die thermal diode offers the most accurate CPU temperature possible.
Otherwise, the 83782D offers similar specs - monitoring for 9 voltages, 3 temperatures, and 3 fan speeds. Case intrusion is still supported as is the CPU VID detection of the correct Vcore. Those 2 additional voltages allow for monitoring of just about every voltage in the system, usually +/-5V, +/-12V, +3.3V, Vcore, VTT, +5Vsb, and Vbat.
Most motherboard manufacturers that choose the 83782D are wise enough to read the CPU temperature from the on-die thermal diode. However, a surprising number still use this in conjunction with an external thermistor near the CPU slot/socket, which leads to slower reaction time for temperature changes.
The Winbond 83783S is simply a stripped down version of the popular 83782D chip and differs primarily in the number of voltages monitored - 6 instead of 9. Typically, this is used to monitor +/-5V, +/-12V, +3.3V, and Vcore. You can still read CPU temperature from the on-die thermal diode, but once again, many manufacturers are still using thermistors. Case intrusion is still supported as is the CPU VID detection of the correct Vcore. Motherboard manufacturers choose this chip over the other Winbond models to cut costs just a bit.
The 83627HF is actually primarily an I/O controller that happens to feature hardware monitoring support. On the hardware monitoring side, it's very similar to the W83782D. It offers the same total of 9 voltage inputs, 3 fan speeds, and 3 thermal inputs. Once again, CPU temperature can be read from the on-die thermal diode, the VID detection of Vcore, and case intrusion are all supported. Since this chip is quite new, most implementations make use of the CPU's on-die thermal diode, but continue to watch out for thermistors for monitoring CPU temperature. The 83627HF does add one interesting feature - the ability to control fan speed as system/CPU temperature varies. Expect this chip to become extremely popular because its price premium over a standard I/O chip without hardware monitoring is minimal.
Like the 83627HF, the 83697HF is also primarily an I/O controller with integrated hardware monitoring features. It's a stripped version of the 83627HF with the main differences being a total of 8 voltages monitored, 2 thermal inputs, and 2 fan speeds. Once again, CPU temperature can be read from the on-die thermal diode, the VID detection of Vcore, case intrusion, and fan speed control are all supported. Since this chip is quite new, most implementations make use of the CPU's on-die thermal diode, but continue to watch out for thermistors for monitoring CPU temperature. We also expect this chip to become quite popular as it’s even cheaper than the 83627HF.
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