M34E02, M34E02-F

Device operation

Doc ID 10367 Rev 10

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3.6

Setting the write-protection

The M34E02 and M34E02-F have a hardware write-protection feature, using the Write

Control (WC) signal. This signal can be driven high or low, and must be held constant for the

whole instruction sequence. When Write Control (WC) is held high, the whole memory array

(addresses 00h to FFh) is write protected. When Write Control (WC) is held low, the write

protection of the memory array is dependent on whether software write-protection has been

set.

Software write-protection allows the bottom half of the memory area (addresses 00h to 7Fh)

to be write protected irrespective of subsequent states of the Write Control (WC) signal.

Software write-protection is handled by three instructions:

●

SWP: Set Write Protection

●

CWP: Clear Write Protection

●

PSWP: Permanently Set Write Protection

The level of write-protection (set or cleared) that has been defined using these instructions,

remains defined even after a power cycle.

3.6.1

SWP and CWP

If the software write-protection has been set with the SWP instruction, it can be cleared

again with a CWP instruction.

The two instructions (SWP and CWP) have the same format as a Byte Write instruction, but

with a different device type identifier (as shown in Table 2). Like the Byte Write instruction, it

is followed by an address byte and a data byte, but in this case the contents are all “Don’t

and specific logical levels must be applied on the other two (E1 and E2, as shown in

Table 2).

3.6.2

PSWP

If the software write-protection has been set with the PSWP instruction, the first 128 bytes of

the memory are permanently write-protected. This write-protection cannot be cleared by

any instruction, or by power-cycling the device, and regardless the state of Write Control

(WC). Also, once the PSWP instruction has been successfully executed, the M34E02 and

M34E02-F no longer acknowledge any instruction (with a device type identifier of 0110) to

access the write-protection settings.

Figure 7.

Setting the write protection (WC = 0)

SDA LINE

AI01935B

ACK

WORD

ADDRESS

VALUE

(DON'T CARE)

ACK

DATA

VALUE

(DON'T CARE)

ACK

CONTROL

BYTE

BUS ACTIVITY

MASTER

BUS ACTIVITY