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MAX6900

I2C-Compatible RTC in a TDFN

Maxim Integrated

MAX6900 Datasheet PDF : 17 Pages

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I2C-Compatible RTC in a TDFN

Table 2. Hex Register Address Definition (continued)

WRITE

ADDRESS/

COMMAND

BYTE

(HEX)

HEX REGISTER ADDRESS/DESCRIPTION

READ

ADDRESS/

COMMAND

BYTE

(HEX)

DESCRIPTION

RAM 8

RAM 9

RAM 10

RAM 11

RAM 12

RAM 13

RAM 14

RAM 15

RAM 16

RAM 17

RAM 18

RAM 19

RAM 20

RAM 21

RAM 22

RAM 23

RAM 24

RAM 25

RAM 26

RAM 27

RAM 28

RAM 29

RAM 30

RAM Burst

POR

CONTENTS

Indeterminate

N/A

on the receiving end. The potential for errors occurs

when the seconds counter increments before all the

other registers are read out. For example, suppose a

carry of 13:59:59 to 14:00:00 occurs during Single

Read operations of the timekeeping registers. The net

data could become 14:59:59, which is erroneous real-

time data. To prevent this with Single Read operations,

read the Seconds register first (initial seconds) and

store this value for future comparison. When the

remaining timekeeping registers have been read out,

read the Seconds register again (final seconds). If the

initial seconds value is 59, check that the final seconds

value is still 59; if not, repeat the entire Single Read

process for the timekeeping registers. A comparison of

the initial seconds value with the final seconds value

can indicate if there was a bus delay problem in read-

ing the timekeeping data (difference should always be

1s or less). Using a 100kHz bus speed, sequential

Single Reads take under 2.5ms to read all seven of the

timekeeping registers plus a second read of the

Seconds register.

The most accurate way to read the timekeeping regis-

ters is a Burst Read. In the Burst Read mode, the main

timekeeping registers (Seconds, Minutes, Hours, Date,

Month, Day, Year) and the Control register are read

sequentially. All of the main timekeeping registers and

the Control register must be read out as a group of

eight registers, with 8 bytes each, for proper execution

10 ______________________________________________________________________________________

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