I/O Expander Code Example

mrjz rose said:

I tested a program but it didn't work.

Why do you want to use an I/O expander? Why don't you use a bigger MSP instead? There are MSPs with up to 83 I/Os. So the effort of programming an expander (slow reaction times, complex handling), the additional cost and also the layout space isn't worth the result.
Except, of course, you want to add all 8 possible expanders to the I2C-bus (giving you 96I/O).

Hi,

I use msp4302619, which support extended temperature range(-55 to 105 ) and there is no MSP with more i/o greater than 48 whit this spec.

and i need a program that runs the 16 bit I/O Expander (PCA9655).

Thanks

 Hi, as Jeans wrote to you, what program you tested, what is wrong? So:

• what you need this program doing
• what speed is necessary to read write to
• is pc interrupt capability needed or just polled?
• how many pc expander do you wish to connect to?
• how long are communication lines?

Missing some or all of these specs none can figure out what you need and your question remain unanswered or just receive first guess then ignored.

Hi,
I want to work with 16 bit I/O expander (PCA9655) because i need more i/o
on msp430f2619. The msp430 and pca9655 are in a small board, and the speed is 400k.

I attach the complete program and schematic for you. In this program i want to load a sample data on LED's

and read the switch.

Thanks.

#include "msp430x26x.h"
#include "TI_USCI_I2C_master.h"

unsigned char timercounter;
unsigned char config_array[3] = { 0x06, 0x00, 0xff };
unsigned char output_array[3] = { 0x02, 0x35, 0xff };



void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT

  BCSCTL1 = CALBC1_8MHZ;
  DCOCTL = CALDCO_8MHZ;

  _EINT();

  TI_USCI_I2C_transmitinit(0x40,0x12);  // init transmitting with USCI
  while ( TI_USCI_I2C_notready() );         // wait for bus to be free
  if ( TI_USCI_I2C_slave_present(0x40) )    // slave address may differ from
  {                                         // initialization
      
    TI_USCI_I2C_transmitinit(0x40,0x12);  // init transmitting with
    while ( TI_USCI_I2C_notready() );         // wait for bus to be free
    TI_USCI_I2C_transmit(3,config_array);       // start transmitting
    
    while ( TI_USCI_I2C_notready() );         // wait for bus to be free
    TI_USCI_I2C_transmit(3,output_array);       // start transmitting  
            
  }
 
  LPM3;
 
}

Hi Robert,
I want to work with 16 bit I/O expander (PCA9655) because i need more i/o
on msp430f2619. The msp430 and pca9655 are in a small board, and the speed is 400k.

I attach the complete program and schematic for you. In this program i want to load a sample data on LED's

and read the switch.

Thanks.


#include "msp430x26x.h"
#include "TI_USCI_I2C_master.h"

unsigned char timercounter;
unsigned char config_array[3] = { 0x06, 0x00, 0xff };
unsigned char output_array[3] = { 0x02, 0x35, 0xff };



void main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT

  BCSCTL1 = CALBC1_8MHZ;
  DCOCTL = CALDCO_8MHZ;

  _EINT();

  TI_USCI_I2C_transmitinit(0x40,0x12);  // init transmitting with USCI
  while ( TI_USCI_I2C_notready() );         // wait for bus to be free
  if ( TI_USCI_I2C_slave_present(0x40) )    // slave address may differ from
  {                                         // initialization
      
    TI_USCI_I2C_transmitinit(0x40,0x12);  // init transmitting with
    while ( TI_USCI_I2C_notready() );         // wait for bus to be free
    TI_USCI_I2C_transmit(3,config_array);       // start transmitting
    
    while ( TI_USCI_I2C_notready() );         // wait for bus to be free
    TI_USCI_I2C_transmit(3,output_array);       // start transmitting  
            
  }
 
  LPM3;
 
}

 Hi, from schematic base address 0x40 is selected, config thru command 06 set direction of led port to output and button to input, command 2 send to output pattern 0x35 word some led on.

 What happen? is program hang somewhere? are you able to single step program and report if complete execution or not?

Hi,

when i debug the program, the routine "TI_USCI_I2C_transmit(3,config_array);" should transmit 3 byte of config_array,

but it only runs for one and PCA9655 doesn't configure.

Best regards

 Hi Where you got Library is also slave one available?

 To cure the problem try just modify the 3 lines on master.c then tell me if it is solved, if not try a breakpoint on IRQService and see what value are on the 3 variables.

signed char byteCtr;
unsigned char *TI_receive_field;
unsigned char *TI_transmit_field;
 

to

volatile signed char byteCtr;
volatile unsigned char *TI_receive_field;
volatile unsigned char *TI_transmit_field;
 

mrjz rose said:

TI_USCI_I2C_transmitinit(0x40,0x12);  // init transmitting with USCI

However, if the transmit only runs for the first byte, it is possible that the loop gets a NACK from the slave. Or (I don't know the exact code) it even gets a NACK when trying to address the slave (wrong address, or clock too fast). The first byte has to be written to TXBUF before the slave has even answered the addressing, due to the double-buffering and clock-stretching mechanisms. So the 'first loop' you see is actually the preparation, and a transfer never starts.

Note that some devices have a timeout (even if this doesn't make much sense on I2C in most situations), so if two bytes are too long apart 8due to debug stops of the processor) they may exit the current transmission and may even discard all data received so far (e.g. in case of multibyte commands).

mrjz rose said:

The address of pca9655 in data sheet is 0x40 but you should consider the address 0x20.