CAT5221

© Catalyst Semiconductor, Inc.

7

Doc. No. MD-2113 Rev. K

Characteristics subject to change without notice

WRITE OPERATION

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 CAT5221. 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 CAT5221

acknowledges once more and the Master generates

the STOP condition, at which time if a nonvolatile 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 CAT5221 initiates the

internal write cycle. ACK polling can be initiated

immediately. This involves issuing the start condition

followed by the slave address. If the CAT5221 is still

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

If the CAT5221 has completed the write operation, an

ACK will be returned and the host can then proceed

with the next instruction operation.

Figure 5. Slave Address Bits

CAT5221

0

1

0

1

A3 A2 A1 A0

*

A0, A1, A2 and A3 correspond to pin A0, A1, A2 and A3 of the device.

** A0, A1, A2 and A3 must compare to its corresponding hard wired input pins.

Figure 6. Write Timing

S

A

C

K

A

C

K

DR WCR DATA

S

T

O

P

P

BUS ACTIVITY:

MASTER

SDA LINE

S

T

A

R

T

A

C

K

SLAVE/DPP

ADDRESS

INSTRUCTION

BYTE

Fixed

Variable

op code

Data Register

Address

Pot/WCR

Address