M34F04 datasheet(10/20 Pages) STMICROELECTRONICS

10 / 20 page

M34F04

10/20

Figure 8. Write Cycle Polling Flowchart using ACK

Minimizing System Delays by Polling On ACK

During the internal Write cycle, the device discon-

nects itself from the bus, and writes a copy of the

data from its internal latches to the memory cells.

The maximum Write time (tw) is shown in Table 9,

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

a polling sequence can be used by the bus master.

The sequence, as shown in Figure 8, 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 device is ready

to receive the second part of the instruction (the

first byte of this instruction having been sent

during Step 1).

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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