SMS45 datasheet(16/20 Pages) SUMMIT

16 / 20 page

SMS45

2079 1.2 05/24/04

SUMMIT MICROELECTRONICS, Inc.

Preliminary Information

Figure 12. Write Flow Chart

Acknowledge Polling

When the SMS45 is performing an internal Write operation

it will ignore any new Start conditions. Since the device will

only return an acknowledge after it accepts the Start the

part can be continuously queried until an acknowledge is

issued, indicating that the internal Write cycle is complete.

See the flow chart for the proper sequence of operations for

polling.

READ OPERATIONS

Read operations are initiated with the R/W bit of the

identification field set to 1. There are two different Read

options: 1. Current Address Byte Read, and 2. Random

Address Byte Read.

Current Address Read (memory only)

The SMS45 contains an internal address counter which

maintains the address of the last word accessed, incre-

mented by one. If the last address accessed (either a

Read or Write) was to address location n, the next Read

operation would access data from address location n+1

and increment the current address pointer. When the

SMS45 receives the Slave address field with the R/W bit

set to 1 it issues an acknowledge and transmits the 8-Bit

word stored at address location n+1. The current address

byte Read operation only accesses a single byte of data.

The Master sets the SDA line to NACK and generates a

stop condition. At this point the SMS45 discontinues data

transmission.

Random Address Read (Register and Memory)

Random address Read operations allow the Master to

access any memory location in a random fashion. This

operation involves a two-step process. First, the Master

issues a write command which includes the start condi-

tion and the Slave address field (with the R/W bit set to

Write), followed by the address of the word it is to Read.

This procedure sets the internal address counter of the

SMS45 to the desired address. After the word address

acknowledge is received by the Master it immediately

reissues a Start condition, followed by another Slave

address field with the R/W bit set to READ. The SMS45 will

respond with an Acknowledge and then transmit the 8 data

bits stored at the addressed location. At this point the

Master sets the SDA line to NACK and generates a Stop

condition. The SMS45 discontinues data transmission and

reverts to its standby power mode.

Sequential READ (Memory Only)

Sequential Reads can be initiated as either a current

address Read or random access Read. The first word is

transmitted as with the other byte Read modes (current

address byte Read or random address byte Read);

however, the Master now responds with an Acknowledge,

indicating that it requires additional data from the SMS45.

The SMS45 continues to output data for each Acknowl-

edge received. The Master terminates the sequential

Read operation by responding with a NACK, and issues

a Stop condition. During a sequential Read operation the

internal address counter is automatically incremented

with each Acknowledge signal. For Read operations all

address bits are incremented, allowing the entire array to

be read using a single Read command. After a count of

the last memory address the address counter will rollover

and the memory will continue to output data.

Operation

a Write?

ACK

Returned

Issue

Address

Proceed

With

Write

Await

Command

Issue Stop

Issue Slave

Address and

R/W = 0

Issue Stop

Write Cycle

In Progress

Yes

Issue Start

2047 Fig12

Yes

I2C PROGRAMMING INFORMATION (CONTINUED)

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