24C32-ISLASHP datasheet(7/12 Pages) MICROCHIP

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DS21061F-page 7

24C32

5.0

ACKNOWLEDGE POLLING

Since the device will not acknowledge during a write

cycle, this can be used to determine when the cycle is

complete (this feature can be used to maximize bus

throughput). Once the stop condition for a write com-

mand has been issued from the master, the device ini-

tiates the internally timed write cycle. ACK polling can

be initiated immediately. This involves the master send-

ing a start condition followed by the control byte for a

write command (R/W = 0). If the device is still busy with

the write cycle, then no ACK will be returned. If the

cycle is complete, then the device will return the ACK

and the master can then proceed with the next read or

write command. See Figure 5-1 for ﬂow diagram

FIGURE 5-1:

ACKNOWLEDGE POLLING

FLOW

Send

Write Command

Send Stop

Condition to

Initiate Write Cycle

Send Start

Send Control Byte

with R/W = 0

Did Device

Acknowledge

(ACK = 0)?

Operation

YES

6.0

READ OPERATION

Read operations are initiated in the same way as write

operations with the exception that the R/W bit of the

slave address is set to one. There are three basic types

of read operations: current address read, random read,

and sequential read.

6.1

Current Address Read

The 24C32 contains an address counter that maintains

the address of the last word accessed, internally incre-

mented by one. Therefore, if the previous access (either

a read or write operation) was to address n (n is any

legal address), the next current address read operation

would access data from address n + 1. Upon receipt of

the slave address with R/W bit set to one, the 24C32

issues an acknowledge and transmits the eight bit data

word. The master will not acknowledge the transfer but

does generate a stop condition and the 24C32 discon-

tinues transmission (Figure 6-1).

6.2

Random Read

Random read operations allow the master to access

any memory location in a random manner. To perform

this type of read operation, ﬁrst the word address must

be set. This is done by sending the word address to the

24C32 as part of a write operation (R/W bit set to 0).

After the word address is sent, the master generates a

start condition following the acknowledge. This termi-

nates the write operation, but not before the internal

address pointer is set. Then the master issues the con-

trol byte again but with the R/W bit set to a one. The

24C32 will then issue an acknowledge and transmit the

eight bit data word. The master will not acknowledge

the transfer but does generate a stop condition which

causes

the

24C32

discontinue

transmission

(Figure 6-2).

FIGURE 6-1:

CURRENT ADDRESS READ

CONTROL

BYTE

DATA n

BUS ACTIVITY

MASTER

SDA LINE

BUS ACTIVITY

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