M24256-BN6 datasheet(7/17 Pages) STMICROELECTRONICS

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M24256, M24128

During the internal write cycle, the SDA input is

disabled internally, and the device does not re-

spond to any requests.

Minimizing System Delays by Polling On ACK

During the internal write cycle, the memory discon-

nects itself from the bus, and copies the data from

its internal latches to the memory cells. The maxi-

mum write time (tw) is shown in Table 10, but the

typical time is shorter. To make use of this, an Ack

polling sequence can be used by the master.

The sequence, as shown in Figure 7, is:

– Initial condition: a Write is in progress.

– Step 1: the master issues a START condition

followed by a Device Select Code (the first byte

of the new instruction).

– Step 2: if the memory is busy with the internal

write cycle, no Ack will be returned and the mas-

ter goes back to Step 1. If the memory has ter-

will fit up to the end of the row, a condition known

as ‘roll-over’ occurs. Data starts to become over-

written (in a way not formally specified in this data

sheet).

The master sends from one up to 64 bytes of data,

each of which is acknowledged by the memory if

the WC pin is low. If the WC pin is high, the con-

tents of the addressed memory location are not

modified, and each data byte is followed by a

NoAck. After each byte is transferred, the internal

byte address counter (the 6 least significant bits

only) is incremented. The transfer is terminated by

the master generating a STOP condition.

When the master generates a STOP condition im-

mediately after the Ack bit (in the “10th bit” time

slot), either at the end of a byte write or a page

write, the internal memory write cycle is triggered.

A STOP condition at any other time does not trig-

ger the internal write cycle.

Figure 7. Write Cycle Polling Flowchart using ACK

WRITE Cycle

in Progress

AI01847C

Operation is

Addressing the

Memory

START Condition

DEVICE SELECT

with RW = 0

ACK

Returned

YES

ReSTART

STOP

DATA for the

WRITE Operation

DEVICE SELECT

with RW = 1

Send Address

and Receive ACK

First byte of instruction

with RW = 0 already

decoded by the device

YES

START

Condition

Continue the

WRITE Operation

Continue the

Random READ Operation

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