DS1305EN+T&R 其他数据使用手册 - Maxim Integrated（美信）

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Keywords: real-time clock, BCD, RTC, binary coded decimal, state machine logic

TUTORIAL 5413

State Machine Logic in Binary-Coded Decimal

(BCD)-Formatted Real-Time Clocks

Sep 17, 2012

Abstract: When developing code to operate a real-time clock (RTC), it is often beneficial to understand

how the clock core operating logic has been defined. This tutorial discusses the counter-chain structure

used in Maxim's binary-coded decimal (BCD)-formatted RTCs. It provides some insight into the expected

insight into the expected chip behavior if improper or illegal contents are somehow installed.

A basic real-time clock counter chain found in many of Maxim's binary-coded decimal (BCD)-formatted

RTCs (such as the DS12885 and DS1302) is illustrated in Figure 1.

Figure 1. RTC counter chain structure.

Each counter register has defined minimum and maximum values, and most are preset to their

appropriate minimums on initial power application. As a natural function of timekeeping, when the

Seconds count reaches the maximum value, the next increment causes a carry to the Minutes register

and the Seconds rolls over to the minimum value. A Minutes rollover carries to the Hours; the Hours