7/15

M34C00

Figure 8. Read Sequence

DEV SEL

DATA 0

AI03717

SEQUENTIAL READ

of first N bytes

DATA N-1

ACK

ACK

ACK

NO ACK

R/W

Table 4. Write Time

Write

WRITE to Array-0 (when not protected)

WRITE to Array-0 (when Write-protected)

0

WRITE to Array-1

WRITE to Array-2

protected.

The

Write-protection

feature

is

activated by writing once to the Protection

Register.

The Protection Register is written with the device

select code set to 0110.1110b (as shown in Figure

9). Address and data bytes must be sent with this

command, but their values are all ignored, and are

treated as Don’t Care. Once the Protection

Register has been written, the Write-protection of

the first 16 bytes of the memory is enabled, and it

is not possible to unprotect these 16 bytes, even if

the device is powered off and on.

When the Protection Register has been written,

the M34C00 no longer responds to the device type

identifier

0110b

for

either

Read

or

Write

operations.

Read Operation

Following a Start condition, the bus master sends

a Device Select code with the RW bit set to 1. The

device acknowledges this, and outputs the byte in

location 00h. The counter is then incremented,

and the device continues to output the next byte in

sequence. To terminate the stream of bytes, the

bus master must

output, and

shown in Figure 8.

The

output

data

comes

from

consecutive

addresses, with the internal address counter

automatically incremented after each byte output.

After the last memory address, the internal

address counter rolls over, to continue reading

from the start of the memory.

Acknowledge in Read Mode

For all Read commands, the device waits, after

each byte read, for an acknowledgment during the

Data (SDA) Low during this time, the device

terminates the data transfer and switches to its

Stand-by mode.

Setting the Write-Protection by Writing to the

Protection Register

The M34C00 has a software Write-protection

function, using the Protection Register, that allows

the bottom 16 bytes of the memory area

(addresses 00h to 0Fh) to be permanently Write-