PIC based "Real Time Clock"

This project was a cost-cutting exercise to reduce the cost of a product while keeping the same functionality.

Introduction

The existing board had a real time clock (RTC) built into a memory chip along with a battery for backup and to run the RTC when the main power failed. Cost savings were made by using a separate Lithium battery, static RAM and dedicated RTC circuit. The RTC circuit was implemented using a Microchip PIC 12C508, which is a small 8-pin device as shown in the photo.

Firmware for the PIC device and for the main board's processor was developed to allow the two devices to communicate. The PIC was powered from the battery backup circuit we designed and contained code written in assembler to act as a simple counter device. The clock signal to the PIC was provided by a watch crystal (32.768kHz). With this in mind, the counter program was designed to count in whole seconds. The main processor was programmed to read from the PIC processor on a schedule, to keep its software clock synchronised with the real time. Using the low I/O PIC devices in this way is common practice and although we cannot re-use the same design for copyright reasons, we can design a solution to your specifications.

The project successfully entered production in 1997 and has been selling worldwide ever since. The circuit and firmware has since been added to another product in manufacture by the same company.

Technology

• Microchip PIC 12C508

Benefits

• Same performance
• Lower manufacturing cost