ADM1266ACPZ-R7 datasheet(23/62 Pages) AD

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Data Sheet

ADM1266

Rev. A | Page 23 of 62

TIME STAMPING

In the black box records, there is an option to save the time of

the black box write, which is beneficial in tracking the time of

the failures. ADM1266 has a real-time counter (RTC) that keeps

track of time. The RTC is reset to zero when ADM1266 is

powered down.

The RTC can be used in two ways. The RTC can be used to

measure the time elapsed since the last time the ADM1266 was

powered up, which is helpful in determining how much time

passed when the system failed after powering up.

In a system, the host controller can send the UNIX® time to the

ADM1266. If a UNIX time is received, the RTC can be used as a

reference to start counting from the UNIX time. When the

UNIX time is set, the device increments from this time and uses

it in black box records to convert to real time. The UNIX time

must be set every time the ADM1266 powers up, because the

RTC resets at power-down.

SETTING UNIX TIME USING SET_RTC

The SET_RTC register consist of six bytes that can be used to

set the time elapsed since January 1, 1970, according to the

UNIX time system. Each LSB represents 15.26 µs. In a system

where multiple ADM1266 devices are connected together, use

the SYNC pin to synchronize the time counter between all

ADM1266 devices.

INTERNAL OSCILLATOR

The internal oscillator in ADM1266 can be used for RTC where

the accuracy of time stamping is not critical. If the RTC is used

for the UNIX time with the internal oscillator, it is recommended

that the system host frequently send the time stamp to the

ADM1266 to synchronize the UNIX time and reduce the time

from drifting.

EXTERNAL OSCILLATOR

In an application where accurate time stamping is required, it is

recommended to use an external 32,768 Hz crystal to generate a

time base for the RTC. An external crystal is connected to the

ADM1266 using the XTAL1 and XTAL2 pins. In a system with

multiple ADM1266 devices, only one crystal is required.

MULTIPLE DEVICE TIME STAMPING

In a system where multiple ADM1266 devices are connected

and an external crystal is used, connect the SYNC pins so that

the RTC is using the same oscillator across all devices. This

configuration minimizes drift in time between devices caused

by variation in oscillating frequency, and requires one external

crystal. Configure the SYNC pin of the device with the external

crystal connected as an output, and the SYNC pin of the other

devices as an input. The SYNC pin configuration can be set

using the GPIO_SYNC_CONFIGURATION (Register 0xE1).

In a multiple device system, the real time can be set by sending

the UNIX time to the SET_RTC register of only one device. The

time is broadcast to the other devices in the system using the

IDB to ensure that all the devices have the same real time.

ADM1266

XTAL1, XTAL2

SYNC

IDSCL IDSDL

3.3V

SCL

SDA

AVDD_CAP

SCL

SDA

SCL

SDA

PMBus

SYNC

IDSCL IDSDL

SYNC

IDSCL IDSDL

Figure 15. Setting Up Time Stamping in a Multidevice Setup

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