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Replace Fixed-Function ICs with Low-Cost Microcontrollers (.PDF Download)

May 29, 2018
Replace Fixed-Function ICs with Low-Cost Microcontrollers (.PDF Download)

Most engineers have known for years that microcontrollers are the best choice in building new digital products. Legacy TTL and CMOS functional logic devices gave way to single-chip MCUs years ago. Yet some operations are still implemented with fixed-function devices because an MCU seems like expensive overkill in certain cases. Not anymore, though. When the price for a tiny MCU comes down to pennies, it’s time to reconsider the use of fixed-function circuits. Here are some ideas to help you go in that direction.

Design Examples

A cheap MCU can replace more discrete logic and mixed-signal devices than you think. One example is a two-bit 8-bit microcontroller that’s able to replace the still popular 555 timer IC. But that’s not all. There are four basic areas where an inexpensive MCU can replace a fixed-function device: communications, system housekeeping, pulse-width modulation (PWM), and timing. The examples below illustrate how it can be done.

Communications

In terms of communications, one example involves the need for two devices to talk to one another. One device uses a UART for external serial communications and another employs a serial peripheral interface (SPI). What’s required is a bridge that acts as a translator for the two devices (Fig. 1). The MCU code translates the protocol of one serial method to another and provides data buffering and half-duplex data transfers. The ability to program the device lets you change the design to optimize it for your application.

1. Here, the MCU acts as a UART-to-SPI bridge.

Another communication application example concerns the use of a single bidirectional line to transfer data between the MCU and a master device. Commonly referred to as 1-wire or SDQ single-wire serial interfaces, this communication peripheral reduces the number of physical hardware connections required while adhering to a protocol that’s easily achievable with a simple MCU. This simple interface is used with external EEPROMs, SHA-1 authenticators, temperature sensors, digital switches, and battery-system monitors.

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