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NicolasC
Joined: 14 Sep 2006
Posts: 27
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| help on I2C_read on MAX6956 |
 Posted: Wed Jan 03, 2007 7:18 am |
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Hello and happy new new year,
When reading port 12 to 19 everything is OK.
But on 20 to 27, the value is once right, once wrong : 255, 63, 255, 63 (all pins are unconnected with pullup activated.
I call mfd_task() periodicaly from main() and read mfd_keys[] for return values.
I had to change i2c_read() to i2c_read(0) to read the proper value.
Can someone explain that I had to disable acknowledge to be able to get the correct value ?
Regards
| Code: |
enum keypad_state { //FSM states for key deboucing
IDLE,
OUTPUT_COL,
DELAY,
INPUT_DATA,
KEY_RELEASE
};
#define Port_12_19 0x4C
#define Port_20_27 0x54
#define _TEMPO_ 0x7FFF
int device_address;
typedef int key_cde;
static key_cde mfd_keys[5]; //list of keys to send through USB
static int16 tempo = _TEMPO_;
static keypad_state mfd_state = IDLE; //machine state for port operation
// Initialise the I2C bus and config register
void mfd_init(int addr )
{
int i;
printf("\r\nI2C init");
i2c_start(); //reset I2C
i2c_stop();
addr+= 0x40; //MAX6956 addresses take the form 100xxxx
device_address = addr; //where xxxx is the user-selected address 0-15.
//write_config_register(0x01); //Transition disable, Global current, no shutdown
i2c_start();
i2c_write( (device_address<<1) & 0xFE );
i2c_write( 0x04 ); //Select Config byte (0x04)
i2c_write( 0x01 ); //Transition disable, Global current, no shutdown
i2c_stop();
//configure port 12 to 22
i2c_start();
i2c_write( (device_address<<1) & 0xFE );
i2c_write( 0x0B ); //set adress for P15, P14, P13, P12 port config
printf("\r\n1:%u", i2c_write( 0xFF )); //set GPIO Inputs With Pullup
printf("\r\n2:%u", i2c_write( 0xFF )); //P19, P18, P17, P16:set GPIO Inputs With Pullup
printf("\r\n3:%u", i2c_write( 0xFF )); //P23, P22, P21, P20:set GPIO Inputs With Pullup
printf("\r\n4:%u", i2c_write( 0xFF )); //P27, P26, P25, P24:set GPIO Inputs With Pullup
i2c_stop();
//init_done = 1;
mfd_state = OUTPUT_COL;
printf("\r\nI2C init done");
}
void write_port(int PortNum, Data)
{
disable_interrupts(GLOBAL);
i2c_start();
i2c_write( (device_address<<1) & 0xFE);
i2c_write( PortNum );
i2c_write( Data );
i2c_stop();
enable_interrupts(GLOBAL);
}
int read_port(int PortNum)
{
int data;
disable_interrupts(GLOBAL);
i2c_start();
i2c_write( (device_address<<1) & 0xFE);
i2c_write( PortNum );
i2c_stop();
i2c_start();
i2c_write( (device_address<<1) | 0x01);
data = i2c_read(0);
printf ("\r\nVal = %u", data);
i2c_stop();
enable_interrupts(GLOBAL);
return data;
}
int mfd_task(void){
switch (mfd_state) {
case IDLE :
mfd_init(0);
break;
default:
if (! --tempo) {
tempo = _TEMPO_;
//mfd_keys[0] = read_port(Port_12_19);
mfd_keys[0] = read_port( Port_20_27 );
return 0;//1;
} else
return 0;
}
}
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Jan 03, 2007 11:13 am |
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| Quote: | I had to change i2c_read() to i2c_read(0) to read the proper value.
Can someone explain that I had to disable acknowledge to be able
to get the correct value ? |
It's part of the i2c specification that the Master should do a NAK on
the last i2c read operation. It's my belief that the person who wrote
those series of data sheets for Maxim just made a mistake. They
left it out.
From the i2c specification:
(Regarding the Master reading from the Slave)
| Quote: |
If a master-receiver is involved in a transfer, it must signal
the end of data to the slave- transmitter by not generating
an acknowledge on the last byte that was clocked out of
the slave. The slave-transmitter must release the data line
to allow the master to generate a STOP or repeated
START condition. |
See section 7.2 "Acknowledge", on page 10 of the i2c specification.
Look about halfway down on the right side of the page, to see the
above quote:
http://www.nxp.com/acrobat_download/literature/9398/39340011.pdf |
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NicolasC
Joined: 14 Sep 2006
Posts: 27
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| Posted: Thu Jan 04, 2007 5:32 am |
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Thanks for your explanations.
It's quite stange that the behaviour is different when reading Port_12_19 and Port_20_27 but never mind : I'll follow the specs and that's it.
Regards |
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