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M14256, M14128

Read Operations

Read operations are independent of the state of

the WC pin. On delivery, the memory content is set

at all “1’s” (FFh).

Current Address Read

The memory has an internal address counter.

Each time a byte is read, this counter is increment-

ed. For the Current Address Read mode, following

a START condition, the master sends a device se-

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

knowledges this, and outputs the byte addressed

by the internal address counter. The counter is

then incremented. The master must

edge the byte output, and terminates the transfer

with a STOP condition, as shown in Figure 8.

Random Address Read

A dummy write is performed to load the address

into the address counter, as shown in Figure 8.

This is followed by another START condition from

the master and the device select is repeated with

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-

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 as follows:

– Initial condition: a Write is in progress.

– Step 1: the master issues a START condition

followed by a device select byte (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

master goes back to Step 1. If the memory 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 in-

struction (the first byte of this instruction having

been sent during Step 1).

Figure 7. Write Cycle Polling Flowchart using ACK

WRITE Cycle

in Progress

AI02165

Next

Operation is

Addressing the

Memory

START Condition

DEVICE SELECT

with RW = 0

ACK

Returned

YES

NO

YES

NO

ReSTART

STOP

Proceed

WRITE Operation

Proceed

Random Address

READ Operation

Send

Byte Address

First byte of instruction

with RW = 0 already

decoded by M14xxx