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STR7 (ARM) - 32-bit Microcontrollers
STR71x I2C communication with M24Cxx EEPROM
Application Note
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Last Updated: 04/03/2008
Pages: 7
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Source file for STR71X I2C communication with M24CXX EEPROM
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AN1782 APPLICATION NOTE
STR71X I2C COMMUNICATION WITH M24CXX EEPROM
INTRODUCTION
This application note gives an example of how to use the STR71x I2C peripheral to communicate with an I2C Protocol-Compatible Electrically Erasable Programmable Read Only Memor y (EEPROM). The example uses the M24C08 EEPROM from STMicroelectronics. The implemented software manages read and write operations between the STR71x I2C interface and the M24C08.
1 STR71X I2C PERIPHERAL
The STR71x I2C peripheral provides both multi master and slave functions, and controls all I2C bus-specific sequencing, protocol, arbitration and timing. It also provides the transfer problem detection feature. The speed of the I2C interface may be selected between standard (0-100KHz) and fast I2C (100-400KHz). The STR71x provides two I2C interfaces I2C0 and I2C1. Only the master characteristics of the STR71x I2C are needed to manage the communication sequencing with EEPROM, which acts as a slave. In this application, only the single master mode is used without error management. To implement the I2C protocol, only 2 bidirectional lines are required, SCL (Serial Clock Line), which carries the synchronization clock and SDA (Serial Data Line), which carries the bit to be transmitted. This line is driven by the device that sends the data. The corresponding port pins have to be configured as alternate function open drain. Please refer to the STR71x reference manual for more details.
2 M24CXX EEPROM
The M24Cxx families of EEPROM are compatible with the I2C protocol. This EEPROM family includes a range of different devices. Table 1 displays the size, the number of devices that can be connected to the I2C bus and the number of blocks in each device. Table 1. M24Cxx EEPROMs family characteristics
Device M24C01 Size (Kbit) 1 Devices per Bus 8 Number of Blocks 1 Rev. 2.0
AN1782/0905 1/7
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I2C COMMUNICATION BETWEEN STR71X AND M24CXX EEPROM
Device M24C02 M24C04 M24C08 M24C016
Size (Kbit) 2 4 8 16
Devices per Bus 8 4 2 1
Number of Blocks 1 2 4 8
3 STR71X/M24C08 COMMUNICATION APPLICATION
3.1 HARDWARE CONFIGURATION Two M24C08 memory chips can be addressed by a microcontroller on the same two wire bus by configuring the M24C08 input E2. In this application the M24C08 E0, E1 and E2 inputs are tied to V3.3 via 10K resistor. The M24C08 is divided into four blocks defined by the two LSB bits of the memory address defined on the following:
M24C08_Block0 ==> ADDRESS 0xA8 M24C08_Block1 ==> ADDRESS 0xAA M24C08_Block2 ==> ADDRESS 0xAC M24C08_Block3 ==> ADDRESS 0xAE
Figure 1. STR71x/M24C08 configuration
V3.3
V3.3
4K7 4K7
STR71x
SDA SCL
M24C08
100 100
E2 SDA SCL E1 E0
10K 10K 10K
3.2 SOFTWARE IMPLEMENTATION In this application note the software modules are developed in C language, with RVDK environment. The software implemented to manage read and write operations between the STR71x I2C interface and the M24C08 is divided in three parts: Write: first, the program writes the contents of a predefined buffer to the memory starting from address 0x00 of Block3,
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I2C COMMUNICATION BETWEEN STR71X AND M24CXX EEPROM
Wait: then, it waits until the write operation is finished, Read: finally it reads the data already written. 3.2.1 Write Operation Before starting the communication, the I2C bus must be in the free state (SCL and SDA must be HIGH). The write sequence is started by getting control of the bus. This action, which puts the bus in busy state, is performed by setting the START bit in the Control Register (CR) in order to generate a START Condition. Then the slave address is written in the Data Register (DR) with the R/Wbit=0. This causes the address to be sent to the slave. The address transmission check is done by looping on the ENDAD flag in Status Register2 (SR2). This flag is cleared by writing 0x20 in the Control Register (CR). Then the master starts sending the data byte by writing it in the Data Register (DR). To transmit a new data byte, the address or the data byte previously transmitted has to be completed correctly. The previous transmission check is done by looping on the BTF flag in Status Register 1 (SR1). This flag is cleared by writing the next byte to be sent in the Data Register. The first byte to be sent is the start address of the destination of the data. A maximum of 16 bytes can be written to the M24C08 in a single write cycle. The write sequence is ended by generating a STOP condition, by setting the STOP bit in the Control Register (CR). This action releases the bus. The following flowchart shows the different steps of the write cycle. Figure 2. Write Operation Flowchart
Begin
Generate START Condition
Send Slave Address((R/W)bit=0)
Send the EEPROM's internal address to write to
Send String
Generate STOP Condition
End
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I2C COMMUNICATION BETWEEN STR71X AND M24CXX EEPROM
Example: This example shows a write of data values 0x05 and 0xE0 to address 0x00 and 0x01 of M24C08 Block3 respectively.
START 0xAE 0 00 0 0x05 0 0xE0 0 STOP
Slave Address(R/W)=0
ACK
Byte Address
ACK
DATA1
ACK
DATA2
ACK
3.2.2 Wait for Write Operation Before starting any new operation with the EEPROM, we wait until the write operation is finished. The EEPROM will send the ACK bit if busy with the write operation, so the processor has to send the EEPROM address continuously until the EEPROM sends the ACK bit. 3.2.3 Read Operation To initiate the communication, the STR71x I2C has to generate a START condition and then send the M24C08 Address (with R/W bit cleared). After checking the correct status of the previous transmission, the Master writes, in the Data Register (DR), the address of the first byte we want to read from the M24C08. The previous byte transmission check is done by looping on the BTF flag in the Status Register 1 (SR1). Then the STR71x I2C has to regenerate the START condition and then write the slave address in the Data Register (DR). This address must be the same as the address sent after the first START condition except that the least significant bit (R/W) must be set. Then a previous byte transmission check is done by looping on the ENDAD flag in Status Register 2 (SR2). After this, the STR71x I2C becomes a receiver for all bytes sent from the M24C08. To receive a new data byte, the previous byte reception has to be completed correctly. The byte reception check is done by looping on the BTF flag in Status Register 1 (SR1). This flag is cleared by reading the Data Register (DR). To close the communication, before reading the last byte from the DR register, set the STOP bit to generate the Stop condition. The interface goes automatically back to slave mode (M/SL bit cleared). In order to generate the non-acknowledge pulse after the last received data byte, the ACK bit must be cleared just before reading the second last data byte.
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I2C COMMUNICATION BETWEEN STR71X AND M24CXX EEPROM
Figure 3. Read Operation Flowchart
Begin
Generate START Condition
Send Slave Address((R/W)bit=0)
Send the EEPROM's address to read from
Re-Generate START
Send Slave Address((R/W)bit=1)
Wait until the byte is received
No
2nd last byte to receive Yes Disable ACK
No Last byte to receive Yes Enable STOP condition generation
Receive next byte
No End of reception Yes End
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I2C COMMUNICATION BETWEEN STR71X AND M24CXX EEPROM
Example: This example shows a read of two bytes from address 0x00 and 0x01 of M24C08 Block3.
START 0xAE Slave Address (R/W)=0 0 ACK 00 Byte Address 0 ACK RESTART 0xAF Slave Address (R/W)=1 DATA1 (Out) DATA1 0 ACK DATA2 (Out) DATA1 1 STOP
NoACK STOP
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I2C COMMUNICATION BETWEEN STR71X AND M24CXX EEPROM
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