#use i2c fast=400000 doesn't output such bitrate

[capfelix]

Hi,

I have trouble getting a correct I2C speed by using #use i2c fast=400000. What I measured on the bus is only around 200khz instead of 400khz as what written in the code. I have to increase it to fast=550000 in order to get close to 400khz.

Any insight about this?

[Ttelmah]

What is your clockrate?.
Are you using software I2C, or hardware I2C?.
What compiler version?.

Best Wishes

[capfelix]

Running at 20Mhz and I'm using Force_HW.

[Ttelmah]

FORCE_HW, means nothing, unless your pin numbers are right...

Post the actual #use I2C line.
Again, what compiler version.
Also, what PIC.

Assuming the #clock defintion is right, you should get 384615Hz (400000 is impossible), but I'd suspect the system is working in software mode.

Best Wishes

[capfelix]

Hi,

I'm using PIC18F4455 and the pin is B0 and B1, which are MSSP I2C pin.

I'm using compiler v4.017.

#include <18F4455.h>
#use delay(clock=20000000)

#use i2c(master, sda=PIN_B0, scl=PIN_B1, FORCE_HW, fast=525000)
#use standard_io(A)
#use standard_io(B)
#use standard_io(C)
#use standard_io(D)

[Ttelmah]

Try it with 3.249.
Seriously, the V4 compilers, are _still_ not working even close to 'right', and are up in the .030's. I would not trust 4.017, to do much right...

Best Wishes