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M24C64-WMW6

64/32 Kbit Serial IC Bus EEPROM

STMicroelectronics 

M24C64, M24C32

Figure 7. Write Cycle Polling Flowchart using ACK

WRITE Cycle

in Progress

START Condition

DEVICE SELECT

with RW = 0

First byte of instruction

with RW = 0 already

decoded by M24xxx

NO ACK

Returned

YES

Next

NO

Operation is

Addressing the

Memory

ReSTART

YES

Send

Byte Address

STOP

Proceed

WRITE Operation

Proceed

Random Address

READ Operation

AI01847

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 9, 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-

minated the internal write cycle, it responds with

an Ack, indicating that the memory is ready to

receive the second part of the next instruction

(the first byte of this instruction having been sent

during Step 1).

Read Operations

Read operations are performed independently of

the state of the WC pin.

Random Address Read

A dummy write is performed to load the address

into the address counter, as shown in Figure 8.

Then, without sending a STOP condition, the mas-

ter sends another START condition, and repeats

the Device Select Code, with the RW bit set to ‘1’.

The memory acknowledges this, and outputs the

contents of the addressed byte. The master must

not acknowledge the byte output, and terminates

the transfer with a STOP condition.

Current Address Read

The device has an internal address counter which

is incremented each time a byte is read. For the

Current Address Read mode, following a START

condition, the master sends a Device Select Code

with the RW bit set to ‘1’. The memory acknowl-

edges this, and outputs the byte addressed by the

8/19

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