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In mains-powered equipment e.g. desktop PC’s, the power consumption and heat dissipation of the CPU are not usually critical factors, as there are normally plenty of watts available from the mains power supply, and forced cooling is relatively easy to implement in a large enclosure. In embedded designs however the rules can be very different; power considerations can be crucial factors in the realisation of a design. To address this need, and leveraging off its strength in the PC market, Intel has introduced a range of low-power embedded Pentium® processors destined specifically for use in embedded applications. Based on Intel's 0.25 micron manufacturing process, these 166MHz and 266MHz processors provide high performance with low power dissipation, running from supply voltages of 1.8, 2.0 and 2.5 volts, and a choice of packages is offered.
There are many potential advantages to be gained from reducing system power; one important one is that overall system MTBF (Mean-Time Between Failures) – an indicator of the reliability of the system - is considerably increased. Since power dissipation is directly proportional to the square of the supply voltage, a reduction in supply voltage from 3.3V to 1.9V reduces power consumption by nearly 70%, without any sacrifice in performance. In some applications developers may be able to use the 166 MHz processor without a heatsink and/or without forced air cooling, which simplifies the design and saves cost and weight. The availability of low-power CPU’s opens up new market areas, especially for battery-operated equipment, however when working with these low-power devices, designers must ensure that the correct voltages are applied to the processor's I/O pins, as these will no longer accept 3.3-V levels. External I/O must either be interfaced via 2.5-V compatible components, like the 430TX-chip set, or adjusted via level shifters to meet the 2.5-V specification requirements. The new low-power Pentium® processors are available in a choice of packages: PPGA (Plastic Staggered Pin Grid Array) and HL-PBGA (High Thermal, Low Profile Plastic Ball Grid Array) with an extended temperature range. The PPGA packaging can be compared with the SPGA package, which is used in Socket 5 or Socket 7 systems. Hitex has introduced a range of adapters for these package types, which enable a quick and reliable connection to be made to the target. For customers who want to evaluate the low-power embedded Pentium® processor, Hitex has developed a new, low-cost evaluation board. This board mounts onto the processor socket of a Socket 5 or Socket 7 based system and contains all the components required for the use in a 3.3-V environment. This is independent of whether the system has a single or a split power plane. The conversion board supports the PPGA packaged low-power devices and generates all the required operating voltages.
One point to watch out for when upgrading to the Pentium® processor from lowlier CPU’s is that there is no support for dynamic bus sizing, so bus widths smaller than 64-bits cannot be directly supported.
Development ToolsSince the low-power Pentium® processor is internally compatible with earlier derivatives, the range of software development tools, including compilers, linkers and monitor debuggers remains the same. If the system is to be operated with an in-circuit emulator, then care must be exercised when it comes to signal levels. For example the JTAG port of the low-power derivatives operates at 2.5 volts, so connecting a 3.3V emulator can result in damage to the processor and/or emulator.
Some further references: Intel Corp: Intel Packaging Databook Intel Corp: http://developer.intel.com |
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