PIC32MX: I2C EEPROM - Revision history

NickMarchuk at 20:17, 1 March 2010

2010-03-01T20:17:02Z

Philip Dames: /* Code */

2010-02-16T22:15:21Z

Code

Philip Dames: /* Code */

2010-02-16T22:13:41Z

Code

Philip Dames: /* Circuit */

2010-02-16T22:03:49Z

Circuit

Philip Dames: /* Circuit */

2010-02-16T22:02:49Z

Circuit

Philip Dames: /* Circuit */

2010-02-16T18:21:29Z

Circuit

Philip Dames: /* Timing */

2010-02-16T17:56:47Z

Timing

Philip Dames: /* Timing */

2010-02-16T17:37:23Z

Timing

MeganWelker: /* Overview */

2010-02-16T17:36:07Z

Overview

MeganWelker: /* Overview */

2010-02-16T17:29:46Z

Overview

@@ Line 1: / Line 1: @@
-== Original Assignment ==
-'''Do not erase this section!'''
-Your assignment is to interface to the I2C 24AA1025 EEPROM chip.
 == Overview ==

@@ Line 73: / Line 73: @@
 == Code ==
-We have created our own library of files to called I2C_EEPROM.h and I2C_EEPROM.h, found below.  This makes use of existing functions in the Peripheral Library (any function with "I2C1" in the title, see chapter 15 of the Peripheral Library Guide for more information.  We also based this code on the example found in C:\Program Files\Microchip\MPLAB C32\examples\plib_examples\i2c\i2c_master\source\i2c_master.c (note that this in in MPLAB C32, NOT MPLAB C32 SUITE which contains an updated version we found to be more confusing).
+We have created our own library of files to called I2C_EEPROM.h and I2C_EEPROM.h, found below.  This makes use of existing functions in the Peripheral Library (any function with "I2C1" in the title, see chapter 15 of the Peripheral Library Guide for more information.  All of our functions use the first I2C bus on the PIC, so to use the other bus you will have to change every instance of I2C1 to I2C2. We also based this code on the example found in C:\Program Files\Microchip\MPLAB C32\examples\plib_examples\i2c\i2c_master\source\i2c_master.c (note that this in in MPLAB C32, NOT MPLAB C32 SUITE which contains an updated version we found to be more confusing).
 Main.c
@@ Line 89: / Line 89: @@
  /*Definitions*************************************************/
- #define BAUD_RATE		100000
+ #define BAUD_RATE		100000   // 100 kHz
  #define BRG_VAL 		((SYS_FREQ/2/BAUD_RATE)-2)  // can use SYS_FREQ because same as peripheral bus freg

@@ Line 72: / Line 72: @@
 == Code ==
+We have created our own library of files to called I2C_EEPROM.h and I2C_EEPROM.h, found below.  This makes use of existing functions in the Peripheral Library (any function with "I2C1" in the title, see chapter 15 of the Peripheral Library Guide for more information.  We also based this code on the example found in C:\Program Files\Microchip\MPLAB C32\examples\plib_examples\i2c\i2c_master\source\i2c_master.c (note that this in in MPLAB C32, NOT MPLAB C32 SUITE which contains an updated version we found to be more confusing).
 Main.c
  /**************************************************************
@@ Line 79: / Line 82: @@
  /*Includes****************************************************/
- #include <string.h> // used for string compare to verify data transmission
+ #include <string.h> // only used for string compare (strcmp) to verify data transmission
  #include <plib.h>
  #include <HardwareProfile.h>
- #include <LCD.h> // used to display for debugging
+ #include <LCD.h> // only used to display for debugging
  #include <I2C_EEPROM.h>
  /*Definitions*************************************************/
  #define BAUD_RATE		100000
- #define BRG_VAL 		((SYS_FREQ/2/BAUD_RATE)-2)
+ #define BRG_VAL 		((SYS_FREQ/2/BAUD_RATE)-2)  // can use SYS_FREQ because same as peripheral bus freg
  /*Global Variables *******************************************/
- unsigned char SlaveAddress = 0x50;
+ unsigned char SlaveAddress;
- short int memoryAddress = 0x0540;
+ short int memoryAddress;
  /*Main Function***********************************************/
@@ Line 97: / Line 100: @@
  {
      char LCDbuffer[33]; // this will store the string for the LCD
-     //unsigned char test[28]="Hello world\nI2C is working!";
+     //unsigned char test[]="Hello world\nI2C is working!";
-     unsigned char test[13]="Hello world!";
+     unsigned char test[]="Hello world!";
      int size = sizeof(test);
      unsigned char readtest[size];
@@ Line 108: / Line 111: @@
      OpenI2C1( I2C_EN, BRG_VAL );
+     memoryAddress = 0x0540;    //arbitrarily chosen for this test
      SlaveAddress = 0x50;	//0b1010(B0)(A0)(A1) 24AA1025 EEPROM address

@@ Line 21: / Line 21: @@
 Pins 1 and 2 are used to define the I2C address of the chip. The address is 0b1010(Location)(A0)(A1), where Location, A0, and A1 are all bits.  Location allows you to select the half of memory to write to, so it will be in the bounds 0x(Location)0000 to 0x(Location)FFFF.  A0 and A1 are the determined by the connections made to pins 1 and 2 on the EEPROM chip (1 is high, 0 is low).  Since there are two pins, up to 4 EEPROMs may be used by a single I2C master.  The first 4 bits of the address are pre-specified by the manufacturer and cannot be changed.  A2 (pin 3) must always be connected to  logical high or the chip will not function.  Pin 7 is write protect; if it is low then write and read operations are allowed, but if this is high then only read operations are allowed.
+IMPORTANT: Pull-up resistors must always be used on the I2C communication lines as shown in the diagram.
 [[Image:I2C.jpg]]

@@ Line 19: / Line 19: @@
 Connection schematic for 24AA1025 Chip.
-Pins 1 and 2 are used to define the I2C address of the chip. The address is 0x1010(Location)(Pin1)(Pin2), where location allows you to write in the memory bounds 0x(Location)0000 to 0x(Location)FFFF.  The first 4 bits of the address are pre-specified by the manufacturer.
+Pins 1 and 2 are used to define the I2C address of the chip. The address is 0b1010(Location)(A0)(A1), where Location, A0, and A1 are all bits.  Location allows you to select the half of memory to write to, so it will be in the bounds 0x(Location)0000 to 0x(Location)FFFF.  A0 and A1 are the determined by the connections made to pins 1 and 2 on the EEPROM chip (1 is high, 0 is low).  Since there are two pins, up to 4 EEPROMs may be used by a single I2C master.  The first 4 bits of the address are pre-specified by the manufacturer and cannot be changed.  A2 (pin 3) must always be connected to  logical high or the chip will not function.  Pin 7 is write protect; if it is low then write and read operations are allowed, but if this is high then only read operations are allowed.
-Pin 7 is write protect.  If this is low then write and read operations are allowed. If this is high then only read operations are allowed.
 [[Image:I2C.jpg]]

@@ Line 66: / Line 66: @@
 |}
-Note, we are able to read a single character using the recieveChar function, but cannot read a string.
+Note, we are only able to read a single character using the recieveChar function, but cannot read a string.
 == Code ==

@@ Line 28: / Line 28: @@
 == Timing ==
+Communication speed is determined by the clock signal and the Baud rate register (BRG).
+<math>F_{clock} = \frac{F_{PB}}{2(BRG+1)}</math>
+This is the rate at which a single bit will be sent/received.  From the data sheet it says the EEPROM supports up to 400 kHz but we found that 100 kHz was more reliable.  Overall timing is limited by the EEPROM's internal write cycle (on the order of 1 ms).
 Table of times for sending data

@@ Line 7: / Line 7: @@
 == Overview ==
-EEPROM stands for stands for Electrically Erasable Programmable Read-Only Memory. It is a type of non-volitile memory that can be used to store little bits of data. Data will remain on EEPROM when power is disconnected, (like an external hardrive).
+EEPROM stands for stands for Electrically Erasable Programmable Read-Only Memory. It is a type of non-volitile memory that can be used to store little bits of data. Data will remain on EEPROM when power is disconnected, (like an external hardrive). The EEPROM chip must be reprogrammed in its entirety, and has a life span in the tens or hundreds of thousands of read/writes.
 You can use the PIC32 to communicate with an EEPROM chip using SPI. This page refers to the usage of a Serial EEPROM.
 To test that the code data was writing and reading correctly, the attached code sends data to the EEPROM through I2C, then from the EEPROM back to the PIC, and out to a LED display screen.
+EEPROM vs. Flash memory: The EEPROM erases the cell one by one, and only erases the 1's back to zero. Flash erases the whole block at once. Since erasing causes wear to the cell, the EEPROM will have a slightly longer lifetime.
 == Circuit ==