AN3355
Application note
Designing an application board compatible with either
standard M24LRxx-R or energy-harvesting M24LRxxE-R devices
Introduction
The goal of this application note is to describe how to design application boards accepting
either standard M24LRxx-R or energy-harvesting M24LRxxE-R devices.
May 2011 Doc ID 018544 Rev 2 1/11
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Contents AN3355
Contents
1 M24LRxx-R and M24LRxxE-R pin-out comparison . . . . . . . . . . . . . . . . 5
2 Designing a board compatible with both devices . . . . . . . . . . . . . . . . . 6
3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2/11 Doc ID 018544 Rev 2
AN3355 List of tables
List of tables
Table 1. Compatibility overview (Pin1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Table 2. Compatibility overview (Pin7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Table 3. M24LRxx-R Device Select byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Table 4. M24LRxxE-R Device Select byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Table 5. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Doc ID 018544 Rev 2 3/11
List of figures AN3355
List of figures
Figure 1. Two families, two pin-outs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Figure 2. Typical schematic of an application powered from M24LRxxE-R. . . . . . . . . . . . . . . . . . . . . 6
4/11 Doc ID 018544 Rev 2
AN3355 M24LRxx-R and M24LRxxE-R pin-out comparison
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1 M24LRxx-R and M24LRxxE-R pin-out comparison
The standard dual-interface M24LRxx-R and the energy-harvesting M24LRxxE-R devices
have small differences in pin-out, which apply to only two pins:
● M24LRxx-R
– Pin1: E0 input (used to define the hardware address of the I²C-bus slave)
– Pin7: E1 input (used to define the hardware address of the I²C-bus slave)
● M24LRxxE-R
– Pin1: Vout (output used to deliver supply voltage to the application)
– Pin7: WIP/Busy output signal (during a Write cycle)
Figure 1. Two families, two pin-outs
When designing a new application, it can be useful to design an application board which can
embed either the standard M24LRxx-R or the energy-harvesting M24LRxxE-R devices.
Doc ID 018544 Rev 2 5/11
Designing a board compatible with both devices AN3355
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2 Designing a board compatible with both devices
The purpose of this application note is to design an application board that accepts either the
standard M24LRxx-R (dual-interface) or the M24LRxxE-R (energy-harvesting) devices.
Let’s see how pin1 and pin7 are used in a typical application based on M24LRxxE-R.
● Pin1: M24LRxxE-R Vout pin, providing a power supply to the application.
This pin is actually connected to the input of the application power supply management
block.
● Pin7: M24LRxxE-R WIP/Busy output.
This pin is connected to one input of the application controller.
Figure 2. Typical schematic of an application powered from M24LRxxE-R
If we substitute the M24LRxxE-R (offering the Energy harvesting function) with an
M24LRxx-R (without energy-harvesting output), we have to check that the two pins 1 and 7
do not induce malfunction or stress in the application.
Conditions applying to pin1:
The M24LRxx-R pin1 is the E0 input. Its logical value is internally read as:
● either E0=1 when directly connected to V
● or E0=0 when directly connected to V
● or E0=0 when left unconnected (HiZ).
6/11 Doc ID 018544 Rev 2
ss
cc
,
,
AN3355 Designing a board compatible with both devices
Comparing this with the M24LRxxE-R requirements, we can see that:
● If pin1 is directly connected to V
cc
:
– OK for the M24LRxx-R,
– not compatible with the M24LRxxE-R: this would short-circuit Vout to V
● If pin1 is directly connected to V
ss
:
cc
.
– OK for the M24LRxx-R,
– not compatible with the M24LRxxE-R: this would short-circuit Vout to V
● If pin1 is left unconnected (HiZ):
ss
.
– OK for the M24LRxx-R.
– OK for the M24LRxxE-R.
Table 1. Compatibility overview (Pin1)
Pin1 M24LRxxx-R M24LRxxE-R Result
Connected to V
Connected to V
Left unconnected
(or connected to a
high impedance)
cc
ss
E0=1 Conflict on Vout Not possible
E0=0 Conflict on Vout Not possible
E0=0 OK OK
We can see that the correct way to design an application accepting either M24LRxx-R or
M24LRxxE-R is to define E0=0 for the M24LRxx-R.
Conditions applying to pin7:
The M24LRxx-R pin7 is the E1 input. Its logical value is internally read as:
● either E1=1 when directly connected to V
● or E1=0 when directly connected to V
● or E1=0 when left unconnected (HiZ).
Comparing this with the M24LRxxE-R requirements, we can see that, consequently:
● If pin7 is directly connected to V
cc
:
– OK for the M24LRxx-R,
– not compatible with the M24LRxxE-R: this would create a short-circuit when
WIP/Busy outputs a 0.
● If pin7 is directly connected to V
ss
:
– OK for the M24LRxx-R,
– not compatible with the M24LRxxE-R: this would force WIP/Busy signal to V
therefore inhibit the WIP/Busy information.
● If pin7 is left unconnected (HiZ):
– OK for the M24LRxx-R,
– OK for the M24LRxxE-R.
ss
,
CC
,
and
ss
Doc ID 018544 Rev 2 7/11
Designing a board compatible with both devices AN3355
Table 2. Compatibility overview (Pin7)
Pin7 M24LRxxx-R M24LRxxE-R Result
Connected to V
Connected to V
cc
ss
E1=1
E1=0
Conflict on
WIP/Busy
WIP/Busy = 0
(always)
Not possible
WIP/Busy info
inhibited
Left unconnected
(or connected to a
E1=0 OK OK
high impedance)
One can see that the correct way to design an application accepting either M24LRxx-R or
M24xxxE-R is to define E1=0.
8/11 Doc ID 018544 Rev 2
AN3355 Summary
3 Summary
When designing an application board that will accept either M24LRxx-R or M24LRxxE-R,
the following rules should be kept in mind:
M24LRxx-R
The Device Select byte (first byte transmitted by the I²C-bus master selecting the device to
be accessed) is defined as shown in Tab le 3 .
Table 3. M24LRxx-R Device Select byte
Device type identifier
(1)
Chip Enable address
b7 b6 b5 b4 b3 b2 b1 b0
Device select code1010E2
1. The most significant bit, b7, is sent first.
2. E0 and E1 are compared against the respective external pins on the memory device.
3. E2 selects either the memory of the system sector.
(3)
E1 E0 RW
(2)
RW
The inputs E0,E1 have to be defined as 0,0 (which is the case when the E0,E1 pins are left
unconnected). The Device Select byte is therefore:
● either 1.0.1.0. 0.0.0.RW (where RW is the Read/Write bit) when addressing data in the
memory array,
● or 1.0.1.0. 1.0.0.RW (where RW is the Read/Write bit) when addressing the system
parameter sector.
M24LRxxE-R
In this case of PCB implementation, the E0 and E1 inputs are connected to the power
supply management block and the WIP/Busy output is connected to a high impedance
input, as shown in Figure 2.
The Device Select byte (first byte transmitted by the I²C-bus master) defines the device to be
selected. The Device Select byte is defined as shown in the following table.
Table 4. M24LRxxE-R Device Select byte
Device type identifier
b7 b6 b5 b4 b3 b2 b1 b0
Device select code1010E2
1. The most significant bit, b7, is sent first.
2. E2 selects either the memory of the system sector.
(1)
Chip Enable address RW
(2)
11RW
The Device Select byte is therefore:
● either 1.0.1.0. 0.1.1.RW (where RW is the Read/Write bit) when addressing data in the
memory array,
● or 1.0.1.0. 1.1.1.RW (where RW is the Read/Write bit) when addressing the system
parameter sector.
Doc ID 018544 Rev 2 9/11
Revision history AN3355
4 Revision history
Table 5. Document revision history
Date Revision Changes
29-Mar-2011 1 Initial release.
24-May-2011 2 Updated Section 3: Summary.
10/11 Doc ID 018544 Rev 2
AN3355
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Doc ID 018544 Rev 2 11/11
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