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Issue #204 July 2007
Are You Up for 16 Bits?
A look at Microchip's Family of 16 -Bit Microcontrollers
by Jeff Bachiochi
Start | Microchip's 16-Bit Family |Eeny, Meeny, Miny, Moe | PIC24F | PIC24H | Need DSP? | dsPIC30/33 | Standard Features | Peripheral Pin Select | DSP | DMA | Jump-Start PCBs | SMPS for $750 | Think, Enter, Win | Sources & PDF
EENY, MEENY, MINY, MOE
When it comes to picking a microcontroller, there are a few factors that can quickly narrow the search. The PCB technology you are designing for will be through-hole, SMT, or a combination of the two. You will be restricted to using an SMT part for many applications that require a microcontroller with high I/O counts. The I/O requirements should be well defined before you choose a microcontroller. This will allow you to zero in on a package size. Through-hole parts come in 18-, 20-, 28-, and 40-pin DIP styles. DIP SMT parts come in 18-, 20-, and 28-pin SOIC and the smaller 20- and 28-pin SSOP style. Tiny leadless QFM styles include 28- and 44-pin packages. The higher-pin-count parts (e.g., the 60-, 80-, and 100-pin TQFPs) are available in both a 0.4-mm and a 0.5-mm lead pitch.
If you looked at all of the 28-pin parts (both 8-bit and 16-bit) offered by Microchip, it would still be overwhelming. That’s why it is helpful to look at what’s available using a couple of different methods. The selection guides on the Microchip web site for 8- and 16-bit microcontrollers are based on a few different factors, including family memory size, memory type, and application features. I prefer using the pin count or application features to narrow down the field.
Once all the peripheral bases have been covered, you may need to estimate memory size or speed requirements. Memory size can be affected by your choice of language, use of tables, and the application’s computational requirements. Speed may be an important factor if you need fast sampling or data throughput. One advantage of having standard-size packages available throughout a product line is the ability to substitute either higher- or lower-performance parts. I often start with the highest performance part for my prototype and adjust my choice downward to fit the final code size and speed necessary to achieve my design requirements.
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