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Toast
Joined: 15 Aug 2019
Posts: 16
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| I2C Scanner problem |
 Posted: Tue Aug 27, 2019 3:55 am |
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Hi everyone , I am testing my device with i2c scanner. However, it could not find any i2c and I investigate into it and found my problem could not finish execute the i2c_write. Basically, the method i used to test is to turn on a LED every line. Although i found the problem, i couldn't understand how it happens. I would like to ask what will cause the problem i encountered and how to solve it ?
| Code: | #include <16F15356.h>
#device ADC=10
#use delay(internal=4MHZ)
#use i2c(Master, sda=PIN_B2, scl=PIN_B1)
#define LED pin_a2
// This function writes the slave address to the i2c bus.
// If a slave chip is at that address, it should respond to
// this with an "ACK". This function returns TRUE if an
// ACK was found. Otherwise it returns FALSE.
int8 get_ack_status(int8 address)
{
int8 status;
i2c_start();
//output_high(LED);
status = i2c_write(address); // Status = 0 if got an ACK
output_high(LED); // The LED did not turn on
i2c_stop();
if(status == 0)
return(TRUE);
else
return(FALSE);
}
//=================================
void main()
{
unsigned int8 i;
unsigned int8 status;
unsigned int8 count = 0;
output_high(pin_B0);
// Try all slave addresses from 0x10 to 0xEF.
// See if we get a response from any slaves
// that may be on the i2c bus.
for(i=0x10; i < 0xF0; i+=2)
{
status = get_ack_status(i);
if(status == TRUE)
{
count++;
delay_ms(2000);
}
}
if(count == 0)
// output_low(LED);
else
// output_high(LED);
while(1);
} |
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temtronic
Joined: 01 Jul 2010
Posts: 9225
Location: Greensville,Ontario
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| Posted: Tue Aug 27, 2019 4:22 am |
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more info needed
1) VDD of PIC...
2) I2C device you're trying to test
3) you have run a '1Hz LED' program to confirm the PIC is operating at correct speed ? |
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Toast
Joined: 15 Aug 2019
Posts: 16
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Toast
Joined: 15 Aug 2019
Posts: 16
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| Posted: Tue Aug 27, 2019 5:01 am |
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| temtronic wrote: | more info needed
1) VDD of PIC...
2) I2C device you're trying to test
3) you have run a '1Hz LED' program to confirm the PIC is operating at correct speed ? |
Sorry but how can I get the frequency formula?
I got a 31Hz LED flashing with the following code
| Code: |
#include <16F15356.h>
#device ADC=10
#use delay(internal=4MHZ)
#INT_TIMER1
void timer1_isr(void)
{
set_timer1(63536);
output_toggle(LED);
}
void main()
{
enable_interrupts(INT_TIMER1);
enable_interrupts(GLOBAL);
setup_timer_1 ( T1_INTERNAL | T1_DIV_BY_8 );
set_timer1(63536);
while(1);
}
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Ttelmah
Joined: 11 Mar 2010
Posts: 19506
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| Posted: Tue Aug 27, 2019 6:56 am |
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It's not going to work.
The device only supports up to 1.95v for VddIO. The output 'high' level
is allowed to go only go up to this. Your PIC at 3.7V, requires an I/O signal
that reaches as least 2.96v. You need a signal buffer between this and
the PIC.
What voltage are you taking your I2C pull up resistors to?. Hopefully not
the 3.7v. This is illegally high for the chip if so. |
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Toast
Joined: 15 Aug 2019
Posts: 16
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| Posted: Tue Aug 27, 2019 7:30 am |
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It does not have any resistor externally connected between the PIC and the ICM-20948  What is the VddIO used for? |
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newguy
Joined: 24 Jun 2004
Posts: 1907
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| Posted: Tue Aug 27, 2019 8:11 am |
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| Toast wrote: | | What is the VddIO used for? |
It's in the name: power supply (Vdd) for the external signals (I/O). |
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dluu13
Joined: 28 Sep 2018
Posts: 395
Location: Toronto, ON
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| Posted: Tue Aug 27, 2019 9:04 am |
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You should read the datasheet carefully, as it tells you all of the operating and maximum voltage ratings of everything on the chip.
For example, VddIO should never reach above 2.5V or else it could immediately and permanently damage the chip. VddIO typical operating condition is even lower, at 1.8V. This is what you should be aiming for.
As for not having the resistors externally connected, that is another reason why you cannot detect your device. I2C protocol specifies that lines are either floating or pulled to ground. You need to have pull up resistors on each line of the I2C bus. Section 4.2 of your device datasheet covers this.
If you google "i2c sparkfun", there is a very helpful tutorial that covers the basics of what is i2c, along with the hardware that you should set up, and the protocol.
However, before wiring any of this up, you had better get yourself some level conversion hardware to convert the logic voltages of your PIC into the logic voltages of your devices so you don't burn it out when you try and connect it. |
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Toast
Joined: 15 Aug 2019
Posts: 16
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| Posted: Tue Aug 27, 2019 10:23 am |
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| Is that the SDA, SCL , AD0 all require the pull up resistors? Can i have them pull up by the software using PIC? |
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dluu13
Joined: 28 Sep 2018
Posts: 395
Location: Toronto, ON
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| Posted: Tue Aug 27, 2019 10:38 am |
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There's the NOFLOAT_HIGH option for the #use i2c directive but I have never used that so I don't know if it works. Why not build the hardware properly?
Besides that, you still need to deal with your voltage levels discrepancy between the PIC and your peripheral. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Aug 27, 2019 10:51 am |
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You also need to tell us if you are using the ICM-20948 chip by itself,
on a board you built, or did you buy a module board with that chip on it ?
If you bought an ICM-20948 module board, then post a link to the website
for that board.
In other words, I want know if you bought a module board, and it has
level shifters on it. |
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Toast
Joined: 15 Aug 2019
Posts: 16
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| Posted: Tue Aug 27, 2019 11:01 am |
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| PCM programmer wrote: | You also need to tell us if you are using the ICM-20948 chip by itself,
on a board you built, or did you buy a module board with that chip on it ?
If you bought an ICM-20948 module board, then post a link to the website
for that board.
In other words, I want know if you bought a module board, and it has
level shifters on it. |
It is the chip by itself |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19506
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| Posted: Tue Aug 27, 2019 11:02 am |
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You most definitely _must not_ let the PIC pull the lines up.
Doing this would destroy the ICM-20948 chip.
You need level shifters.
You also need a supply for VddIO. Level shifters, and pull up resistors
to VddIO on the ICM-20948, and pull ups to 3.7v on the PIC side.
Sparkfun do a little board with the level shifter circuit. |
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Toast
Joined: 15 Aug 2019
Posts: 16
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| Posted: Tue Aug 27, 2019 11:13 am |
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| dluu13 wrote: | There's the NOFLOAT_HIGH option for the #use i2c directive but I have never used that so I don't know if it works. Why not build the hardware properly?
Besides that, you still need to deal with your voltage levels discrepancy between the PIC and your peripheral. |
Sorry the VDD of my PIC is 3.3V.
For the voltage level conversion, can i use the voltage divider?
| Code: |
+3.3v
|
<
> 10k
<
ICM20948 |
vddIO pin | 12k
----- -------------- ---------v^v------- || GND
Vout / 3.3 = 12k / (10k+12k)
Vout = 1.8V
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newguy
Joined: 24 Jun 2004
Posts: 1907
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| Posted: Tue Aug 27, 2019 11:14 am |
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| Depends. How much current does the VddIO pin draw? |
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