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	WHAT'S YOUR ENGINEERING QUOTIENT?
•Take a Swing! Problem 3—Frugalson has a simple control application that requires 32 TTL/CMOS input pins and 32 output pins. The actual processing can be done by a $2 microcontroller, but the $2 microcontroller does not have enough I/O pins. Does Frugalson need to upgrade to a $50 embedded controller board? Answer: Not necessarily. If the application can read all inputs in one shot and write all outputs in one shot, and there is no tight timing requirement, Frugalson can consider using serial registers. The design can use four 74HC595s for output pins and four 74HC166s for input pins. The 74HC595s can be daisy chained, and so can the 74HC166s. The daisy chain topology also makes the design easier to route than bus-based designs. Note that the two daisy chains can share the same serial clock signal and load/latch signal. For applications that switch voltage and current higher than TTL/CMOS signal levels, the TPIC6B595 is a ruggedized shift register that can switch up to 50 V and 150 mA with built-in clamp diodes. 4-00 For questions or comments about Test Your EQ, e-mail eq@circuitcellar.com.