AN3057

Recommendations when developing the M24LRxx application software

Doc ID 16239 Rev 4

13/15

3.2

Issuing a command through the RF channel

Case 1: the M24LRxx is processing an I²C command

If the M24LRxx is processing a command from the I²C channel, no command issued on the

RF channel will be executed (the RF command will not provide any response) when the

M24LRxx is I²C busy.

The application’s RF software should include an “I²C busy polling loop” (including a timeout

as there might not be a response) when issuing an RF command. In this way, the RF

command is always correctly executed once the I²C commands under execution are

completed.

Case 2: the M24LRxx application is powered on

The first condition for a safe design of an M24LRxx application is that all the sensitive data

stored in the M24LRxx memory is protected with RF passwords, so that a spurious RF

command could not modify this data.

The second condition for a safe application design is that the application Master fully

supplied, and the RF field drops to zero while the M24LRxx is decoding an RF command,

Figure 10).

Depending on the application’s RF data transfer flow, it might also be wise to add a third

level of safety:

●

blindly send a Reset to Ready command before sending any new RF command

sequence: this will reset the M24LRxx logic

●

once an RF session (several commands) is completed, blindly send a Write-sector

Password command with a wrong password value: this will set the internal flag defining

the status of the presented password (flag set as “wrong password presented”).

Case 3: the M24LRxx application is not powered

This is the typical case where the application is packed in a box (at the end of the production

line) and the data update is performed through RF.

The only condition for a safe application design is that the sensitive data stored in the

M24LRxx memory is protected with RF passwords, so that a spurious RF command could

not modify this data.

Table 4.

Command processed

by the M24LRxx

Device status

I²C command

I²C busy state

RF command

To be avoided in cases where the RF field might

drop to 0 (RF=0 does not reset the RF logic of the