Help communicating with I2C octal registers and switches

lpcware — Mon, 02 Nov 2020 13:39:07 GMT

Content originally posted in LPCWare by jtor on Fri Feb 06 12:54:25 MST 2015
Hi everyone,

I have an LPC2368 with a Keil Dev Board. I am needing assistance in reading a couple I2C devices.

I have been trying to communicate with a PCA9557 as well as a PCA9547D both made by NXP. Listed below are links to the data sheets.

www.nxp.com/documents/data_sheet/PCA9557.pdf - pg. 9 of 30

http://www.nxp.com/documents/data_sheet/PCA9547.pdf - pg. 6 of 30

When configuring and reading these registers, my status bits are returning okay, but my expected output buffers are not accurate.

I want to know if my method of communicating with these specific devices is correct, which I do not think so.. To illustrate this, I am going to have to post some code.

//CONFIGURE REGISTER PORTION
uint8 configOctalRegister(void)
{
uint8 stat;
uint8 buff[2] = { 0x03, 0x7F }; // 0x03 = CONIG REGISTER, 0x7F = pins 1 - 6 are inputs and pin 7 is an output

stat = writeI2C( ADDR_1, 2, buff, 1 ); //octalRegister1

return stat;
}

int writeI2C(uint8 addr, uint8 sz, uint8 *buff, uint8 bus)
{
  uint8 i;
  uint16 stat;

  /* shift address to bits 7-1; bit 0 is R/W */
  I2CMasterBuffer[0] = addr<<1;

  /* write "size" + 1 uint8 for address */
  I2CWrLength = sz + 1;
  I2CRdLength = 0;
  for (i = 0; i < sz; i++)
I2CMasterBuffer[i+1] = buff;
    
  stat = I2CEngine(bus);
  return stat;
}

I will now show the process of how I read the input register. My I2C master buffer is this, in order, [0] = ADDR ; [1] = 0x00 (input reg) ; [2] = READ ADDR

uint8 readExpanderPins( uint8 addr)
{
uint8 stat;
uint8 buff;
        buff = 0x00; //read the input port register

        stat = write_readI2C( ADDR_1, 1, 0x00, &buff, 1 );  //passing the addr, readSize, offset, buffer, bus
if(!stat)
{
bit2status = ( buff & 0x04 ); //buff[2]; bit2
bit3tatus = ( buff & 0x08 ); //buff[3]; bit3
bit4status = ( buff & 0x01 ); //buff[4]; bit4
bit5status = ( buff & 0x20 ); //buff[5]; bit5
bit6status = ( buff & 0x40 ); //buff[6]; bit6
}
return stat;

int write_readI2C(uint8 addr, uint8 sz, uint8 offset, uint8 *buff, uint8 bus)
{
  uint8 i;
  uint16 stat;

  /* shift address to bits 7-1; bit 0 is R/W */
  I2CMasterBuffer[0] = addr<<1;

  /* write 2 size: I2C address + offset to read */
  I2CWrLength = 2;
  I2CMasterBuffer[1] = offset;
    
  /* now load read command */
  I2CMasterBuffer[2] = addr<<1 | RD_BIT;
  I2CRdLength = sz;

  stat = I2CEngine(bus); 
  if (stat)
    return stat;

  if (RdIndex == 0) //no data was read
return FAIL; //(I2C_ERR_MASK | RD_ERR);
  for ( i = 0; i < sz; i++ )
    buff = I2CMasterBuffer[i+3];

  return stat; 
}

I will not show the interrupt routine soloely based on I know it works for reading and writing to other I2C devices such as temperature sensor. Plus this post is already long enough.

I appreciate any expert help on my problem. If any more content is needed just let me know.

topic Help communicating with I2C octal registers and switches in LPC Microcontrollers

Help communicating with I2C octal registers and switches