CAT5259

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7

Acknowledge

After a successful data transfer, each receiving device is

required to generate an acknowledge. The Acknowledging

device pulls down the SDA line during the ninth clock cycle,

signaling that it received the 8 bits of data.

The CAT5259 responds with an acknowledge after

receiving a START condition and its slave address. If the

device has been selected along with a write operation, it

responds with an acknowledge after receiving each 8-bit

byte.

When the CAT5259 is in a READ mode it transmits 8 bits

of data, releases the SDA line, and monitors the line for an

acknowledge. Once it receives this acknowledge, the

CAT5259 will continue to transmit data. If no acknowledge

is sent by the Master, the device terminates data transmission

and waits for a STOP condition.

WRITE OPERATIONS

In the Write mode, the Master device sends the START

condition and the slave address information to the Slave

device. After the Slave generates an acknowledge, the

Master sends the instruction byte that defines the requested

operation of CAT5259. The instruction byte consist of a

four-bit opcode followed by two register selection bits and

two pot selection bits. After receiving another acknowledge

from the Slave, the Master device transmits the data to be

written into the selected register. The CAT5259

acknowledges once more and the Master generates the

STOP condition, at which time if a non-volatile data register

is being selected, the device begins an internal programming

cycle to non-volatile memory. While this internal cycle is in

progress, the device will not respond to any request from the

Master device.

Acknowledge Polling

The disabling of the inputs can be used to take advantage

of the typical write cycle time. Once the stop condition is

issued to indicate the end of the host’s write operation, the

CAT5259 initiates the internal write cycle. ACK polling can

be initiated immediately. This involves issuing the start

condition followed by the slave address. If the CAT5259 is

still busy with the write operation, no ACK will be returned.

If the CAT5259 has completed the write operation, an ACK

will be returned and the host can then proceed with the next

instruction operation.

Write Protection

The Write Protection feature allows the user to protect

against inadvertent programming of the non-volatile data

registers. If the WP pin is tied to LOW, the data registers are

protected and become read only. Similarly, the WP pin is

going low after start will interrupt non-volatile write to data

registers, while WP pin going low after an internal write

cycle has started will have no effect on any write operation.

The CAT5259 will accept both slave addresses and

instructions, but the data registers are protected from

programming by the device’s failure to send an

acknowledge after data is received.

STOP

CONDITION

START

CONDITION

ADDRESS

ACK

8TH BIT

BYTE n

SCL

SDA

Figure 3. Write Cycle Timing

Figure 4. Start/Stop Condition

START CONDITION

SDA

STOP CONDITION

SCL