PIC32MX: I2C External RAM

Original Assignment

Do not erase this section!

Your assignment is to use I2C communication to send data from the PIC32 to a PCF8570P SRAM chip.

Overview

This page discusses work toward sending data to a PCF8570P SRAM chip. Basic I2C communication information, chip data, circuit diagram, and a partially functioning code are given. Prior to the code is a brief explanation of where the code is failing and why no data is being transmitted between the PIC 32 and the PCF8570P.

Circuit

Include a schematic and give any part numbers. A photo of your circuit is OK, but not as a replacement for a schematic.

Code

The following code generates the proper clock and data pulses from the PIC32, however, the PCF8570P chip continuously failed to return an "Acknowledge" bit suggesting that the chip was not processing the data being sent to it by the PIC.

DO NOT USE THE FOLLOWING CODE AS WRITTEN - IT DOES NOT WORK - MODIFY BEFORE USING

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// INCLUDES

1. include <HardwareProfile.h>
2. include <HardwareProfile_NU32.h>
3. include <plib.h>

// Configuration Bit settings // SYSCLK = 80 MHz (8MHz Crystal/ FPLLIDIV * FPLLMUL / FPLLODIV) // PBCLK = 50 KHz // Primary Osc w/PLL (XT+,HS+,EC+PLL) // WDT OFF // Other options are don't care //

1. pragma config FPLLMUL = MUL_20, FPLLIDIV = DIV_2, FPLLODIV = DIV_1, FWDTEN = OFF
2. pragma config POSCMOD = HS, FNOSC = PRIPLL, FPBDIV = DIV_2

// DEFINES

1. define SYSCLK (80000000)
2. define PBCLK (SYSCLK/2) // set PBCLK to 800 KHz

1. define Fsck 50000
2. define BRG_VAL ((PBCLK/2/Fsck)-2)

1. define Nop() asm( "nop" )

/////////////////////////////////////////////

void i2c_wait(unsigned int cnt) { while(--cnt) { Nop(); Nop(); } }

/////////////////////////////////////////////

int main(void)

{ while(1) { unsigned char SlaveAddress; char i2cData[0]; int DataSz;

//Enable channel OpenI2C1( I2C_EN, BRG_VAL );

SlaveAddress = 0x50; (0b01010000)

i2cData[0] = ((SlaveAddress << 1) | 0 ); //slave address and write command i2cData[1] = 0x05; //word address i2cData[2] = 0xAA; //data bits 10101010 DataSz = 3;

StartI2C1(); //Send the Start condition to the clock and data lines IdleI2C1(); //Wait to complete

MasterWriteI2C1 (i2cData[0]); //sends first string of data to PCF8570P IdleI2C1(); if( I2C1STATbits.ACKSTAT ) //looks for acknowledge low bit to be returned break;

MasterWriteI2C1 (i2cData[1]); IdleI2C1(); if( I2C1STATbits.ACKSTAT ) break;

MasterWriteI2C1 (i2cData[2]); IdleI2C1(); if( I2C1STATbits.ACKSTAT ) break;

StopI2C1(); //sends the stop condition to the PCF8570P clock and data lines IdleI2C1();

///////////////////////////////////////////////////////////

//Reading Data from the PCF8570P //First sends write command to write which word the PIC wants to read from

i2cData[0] = (SlaveAddress << 1) | 0; i2cData[1] = 0x05; DataSz = 2;

StartI2C1(); //Send the Start Bit IdleI2C1(); //Wait to complete

MasterWriteI2C1 (i2cData[0]); IdleI2C1(); if( I2C1STATbits.ACKSTAT ) break;

MasterWriteI2C1 (i2cData[1]); IdleI2C1(); if( I2C1STATbits.ACKSTAT ) break;

RestartI2C1(); //restarts the PCF8570P IdleI2C1();

MasterWriteI2C1( (SlaveAddress << 1) | 1 ); //transmit slave address and read command IdleI2C1();

MasterWriteI2C1(i2cData[1]); IdleI2C1();

unsigned char i2cbyte; i2cbyte = MasterReadI2C1(); //PIC reads data from PCF8570P

StopI2C1(); IdleI2C1();

} }