SMS1242 datasheet(8/11 Pages) SUMMIT

8 / 11 page

SMS1242

2038 2.0 6/8/00

SUMMIT MICROELECTRONICS, Inc.

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

2038 Flow01 2.0

Yes

Should the master transmit more than 16 bytes, prior to

generating the STOP condition, the address counter will

“roll over” and the previously written data will be overwrit-

ten.

As with the byte-write operation, all inputs are

disabled during the internal write cycle. Refer to Figure 8

for the address, ACKnowledge and data transfer se-

quence.

Acknowledge Polling

When the SMS1242 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 diagram 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

2. Random Address Byte Read

Current Address Read

The SMS1242 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

Figure 8. Memory Operation

X X X

Typical Write Operation

Typical Read Operation

Master

SDA

Slave

Master

SDA

Slave

2038 T Fig08 2.0

MEMORY OPERATION (Continued)

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