Recommendations when developing the M24LRxx application software

AN3057

12/15

Doc ID 16239 Rev 4

Application hardware architecture

The application Master should control the I²C bus lines and the power supply line so as to

keep full control of the M24LRxx. Figure 10 shows a typical hardware schematic.

Figure 10.

Optimal hardware schematic of an M24LRxx application

This type of hardware architecture is optimal in applications where power saving is a key

feature (like portable applications supplied from a battery). The supply voltage can be

directly delivered to an ultralow power microcontroller (for instance the STM8L, information

available from http://www.st.com/mcu/). This implementation makes it possible to keep the

application supply current in the 1 µA range (value of the STM8L supply current when in the

Active-Alt mode) and:

●

the application saves power when in the Standby mode, as the battery does not supply

the standby current to the M24LRxx (40 µA) nor the current through the SDA pull-up

resistor

●

Master only when an I²C request is being processed)

3.1.3

An I²C request was interrupted

A Start condition defines the I²C channel as busy until the completion of the I²C command

(Stop condition). Therefore, if, for some uncontrolled reasons, the I²C bus master sends a

single Start condition (due to a glitch on the bus or some other unpredictable conditions),

the I²C bus might possibly remain busy indefinitely. The resulting I²C busy state inhibits the

decoding of any subsequent I²C and/or RF requests.

The I²C busy state is reset either by:

●

decoding a device select byte different from 1010 XXXXb

●

decoding a Stop condition

●

The best way for the I²C bus Master to clear a spurious busy state is to periodically issue a

[Start+Stop] sequence.

Note:

In noisy applications, ST recommends to implement the “9 Start + 1 Stop” sequence

described in AN1471 (available from the ST website: www.st.com).

I/O

SDA

SCL

M24LRxx

I²C bus

Master

C = 10 nF

R=10

Ω

Battery

ai17545v2

Application master