AT73C224-H_14 Datasheet, PDF(13/75 Page) ATMEL Corporation – Ultra-low Power Real-time Clock (RTC) and Backup Battery Management

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AT73C224-H_14 Datasheet, PDF (13/75 Pages) ATMEL Corporation – Ultra-low Power Real-time Clock (RTC) and Backup Battery Management

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AT73C224

5.3 Digital Control and Protocol

The AT73C224-x family offers a choice of devices in static mode or dynamic mode (see Table 1-

1 on page 2). In dynamic mode, the user can manage the chip via SPI or TWI. The selection

between SPI or TWI is done at start-up via the D4 pin (see Section 5.3.2 on page 14).

5.3.1

Static Mode

When the AT73C224-x is established in Static Mode, the digital interface signals, D1 to D4,

directly drive the enable of the four supplies. During start-up, these enable signals are driven by

the internal state machine. To ensure a safe transition between the start-up state and the estab-

lished state, a handshake protocol must be respected. This transition period is especially

important in a microcontroller environment, as the microcontroller controlling the D1-D4 signals

may require an unknown period of time to actually drive these pins.

In Static Mode, the ITB/RDY pin is configured as an input with controllable pull-up resistor. When

the internal state machine completes the supply start-up, it latches the value of ITB/RDY and

then sets the POK signal to 1. This means that start-up is accomplished. The state machine then

checks for changes on ITB/RDY. If no changes are detected, the control of the four supply chan-

nels remains with the state machine. If a change is detected the internal pullup is disconnected

and the control is passed on to D1-D4, with the assignment shown in Table 5-2 below.

Table 5-1. D1-D4 Signal Assignment

Digital Interface Signal

Supply Enable

Enables BOOST1

Enables BUCK2

Enables LDO3

Enables LDO4

The illustrations in Figure 5-3, Figure 5-5 and Figure 5-5 represent possible static mode

scenarios.

Figure 5-3. Fully Static Mode

0 or 1

ITB/RDY

POK

Open or 1

Power OK

Since ITB/RDY is 1 or open (weak internal pullup), the state of each supply channel is deter-

mined by the internal state machine (Automatic Start-up sequence and default values for the

three power supplies). In this configuration, the 4th power supply is off and can not be used. D1-

D4 is not considered, but must be valid. The POK signal can be used as a global system reset.

6266AâPMAACâ08-Sep-08

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