14

SMS44

2047 2.3 10/23/00

SUMMIT MICROELECTRONICS, Inc.

Acknowledge Polling

When the SMS44 is performing an internal WRITE opera-

tion 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.” T here are two different read

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

Address Byte Read

Figure 11. Write Flow Chart

Current Address Read (memory only)

The SMS44 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 incre-

ment the current address pointer. When the SMS44

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 does not acknowledge the transfer, but does

generate a stop condition.

At this point, the SMS44

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 condition

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 SMS44

to the desired address. After the word address acknowl-

edge 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 SMS44 will respond with

an acknowledge and then transmit the 8 data bits stored

at the addressed location. At this point the master does not

acknowledge the transmission but does generate the stop

condition. The SMS44 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 ACKnowl-

edge, indicating that it requires additional data from the

SMS44. The SMS44 continues to output data for each

ACKnowledge received. The master terminates the se-

quential READ operation by not responding with an AC-

Knowledge, and issues a stop condition. During a sequen-

tial read operation the internal address counter is auto-

matically 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 ‘roll-over’ and the memory will con-

tinue to output data.

Next

Operation

a Write?

ACK

Returned

Issue

Address

Proceed

With

Write

Await

Next

Command

Issue Stop

Issue Slave

Address and

R/W = 0

Issue Stop

Write Cycle

In Progress

Yes

No

Issue Start

2047 Fig11 2.1

Yes

No