M34A02 datasheet(7/15 Pages) STMICROELECTRONICS

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M34A02

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

overwritten (in a way not formally specified in this

data sheet).

The bus master sends from one up to 16 bytes of

data, each of which is acknowledged by the

memory if Write Control (WC) is Low. If Write

Control (WC) is High, the contents 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 4 least significant bits only) is

incremented. The transfer is terminated by the bus

master generating a Stop condition.

Minimizing System Delays by Polling On ACK

During the internal Write cycle, the device

disconnects itself from the bus, and copies the

data from its internal latches to the memory cells.

The maximum Write time (tw) is shown in Table 6,

but the typical time is shorter. To make use of this,

an Ack polling sequence can be used by the bus

master.

The sequence, as shown in Figure 7, is:

– Initial condition: a Write cycle is in progress.

– Step 1: the bus master issues a Start condition

followed by a Device Select code (the first byte

of the new instruction).

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

Write cycle, no Ack will be returned and the bus

master goes back to Step 1. If the device has

terminated 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 Write Control (WC) signal.

Figure 8. 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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