Running Bus at Low Speed- I2C bit banging

i2c

I am implementing I2C using Bit bang. The slave can accept maximum baud rate of 400kbps. Iam not using external pull up, which is required because of which the fall/rise are not accordingly. I read somewhere fall/rise time can corrected by using external pull up or by running bus at very low speed. Can someone please tell what does running the bus slow means.
Please guide me on this.

Thanks

Best Answer

Measure the rise time of your SCL and SDA signals with an oscilloscope.

Then "slow" means slow enough for SCL and SDA to achieve legal logic levels after you release them.

Be aware that if this results in extremely slow transactions, some devices might fail due to time-out behavior.

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Electronic – What kind of issues might I face when moving from 400 kHz I2C to 1 MHz I2C

If you are going to run an I2C bus with mixed speeds, and you have devices on the bus that can only work at 400 KHz and below, then they must be disabled somehow (e.g. powering them down, so their I2C bus leads will be tristated) when running the bus at the 1 MHz speed, since they will not be able to parse the high-speed addresses and may respond incorrectly.

Electronic – Strange I2C Behaviour

It looks to me that you're ORing terms that you need to be ANDing. I2C_ON is 0xFFFF, so the register is going to be all 1's.

Take a look at the i2c.h file for PIC24:

#define I2C_ON                      0xFFFF /*I2C module enabled */

No matter what else you put in the configuration word, they're all going to be 1. Many settings you need (general call off, 7-bit address, etc.) need their corresponding bits to be zero.

Here's how I init the I2C peripheral on a dsPIC33 (essentially the same peripheral and same library calls):

OpenI2C1(I2C1_ON & I2C1_IDLE_CON & I2C1_7BIT_ADD & I2C1_STR_EN & I2C1_SLW_DIS & I2C1_GCALL_DIS & I2C1_SM_EN & I2C1_IPMI_DIS, clk);

Also bear in mind that the clock argument should be unsigned int - not 4.2 :)

(When in doubt, don't use the library call and manually set the SFR bits yourself.)

Best Answer

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