4285FZ View Datasheet(PDF) - Intersil

Part Name

Description

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4285FZ

CPU Supervisor with 128K EEPROM

Intersil 

X4283, X4285

Serial Start Condition

All commands are preceded by the start condition,

which is a HIGH to LOW transition of SDA when SCL

is HIGH. The device continuously monitors the SDA

and SCL lines for the start condition and will not

respond to any command until this condition has been

met. See Figure 6.

Figure 6. Valid Start and Stop Conditions

Serial Stop Condition

All communications must be terminated by a stop

condition, which is a LOW to HIGH transition of SDA

when SCL is HIGH. The stop condition is also used to

place the device into the Standby power mode after a

read sequence. A stop condition can only be issued

after the transmitting device has released the bus. See

Figure 6.

SCL

SDA

Start

Serial Acknowledge

Acknowledge is a software convention used to indi-

cate successful data transfer. The transmitting device,

either master or slave, will release the bus after trans-

mitting eight bits. During the ninth clock cycle, the

receiver will pull the SDA line LOW to acknowledge

that it received the eight bits of data. Refer to Figure 7.

The device will respond with an acknowledge after

recognition of a start condition and if the correct

Device Identifier and Select bits are contained in the

Slave Address Byte. If a write operation is selected,

the device will respond with an acknowledge after the

receipt of each subsequent eight bit word. The device

Figure 7. Acknowledge Response from Receiver

SCL from

Master

1

Data Output

from

Data Output

from Receiver

START

Stop

will acknowledge all incoming data and address bytes,

except for the Slave Address Byte when the Device

Identifier and/or Select bits are incorrect.

In the read mode, the device will transmit eight bits of

data, release the SDA line, then monitor the line for an

acknowledge. If an acknowledge is detected and no

stop condition is generated by the master, the device

will continue to transmit data. The device will terminate

further data transmissions if an acknowledge is not

detected. The master must then issue a stop condition

to return the device to Standby mode and place the

device into a known state.

8

9

Acknowledge

10

FN8121.1

May 23, 2006

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