I2C software library request

[Mike]

The current I2C software library supports three speeds: 1MHz, 400kHz, and 100kHz.  But many aftermarket I2C devices can go much faster than that, such as the small OLED displays.

Long ago I modified my local copy of the library to support an "unlimited" speed and I'm asking that this option be added to jallib.  See below.

Regards,

Mike

procedure  _i2c_wait() is
   
   if i2c_bus_speed == 255 then
      return
   if _i2c_bus_speed == 10 then
      ; i2c_1MHz
      delay_1us()
      return
   elsif _i2c_bus_speed == 4  then
      ; i2c_400kHz
      delay_2us()
      return
   else                          
      ; i2c_100kHz
      delay_5us()
      return
   end if
   
end procedure

[Mike]

The code should have been this:

procedure  _i2c_wait() is
   
   if i2c_bus_speed == 255 then
      return

   elsif _i2c_bus_speed == 10 then

      ; i2c_1MHz
      delay_1us()
      return
   elsif _i2c_bus_speed == 4  then
      ; i2c_400kHz
      delay_2us()
      return
   else                          
      ; i2c_100kHz
      delay_5us()
      return
   end if
   
end procedure

[Rob CJ]

Hi Mike,

Seems like a good addtion. I updated the library with your suggestion. If you are OK with it, I will add it to Jallib.

I also added some extra info about the bus speeds.

Kind regards,

Rob

---

Van: 'Mike' via jallib <jal...@googlegroups.com>
Verzonden: zaterdag 28 februari 2026 16:56
Aan: jallib <jal...@googlegroups.com>
Onderwerp: [jallib] Re: I2C software library request

 

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[Mike]

Hi Rob,

I tested the "no delay" speed setting on a 12F683 running on the 8MHz internal oscillator and connected to a 128x32 I2C OLED display and it worked just fine.  I'll try faster (crystals) at some point, as well as the 32MHz internal oscillator of the 12F1840 and 16F1825 that I know I have.

Regards,

Mike

[Rob CJ]

Hi Mike,

Thanks for testing. I added the update to Github. I saw that the bee package was already made so it will be in the next version.

Kind regards,

Rob

---

Van: 'Mike' via jallib <jal...@googlegroups.com>

Verzonden: zaterdag 28 februari 2026 23:14
Aan: jallib <jal...@googlegroups.com>
Onderwerp: Re: [jallib] Re: I2C software library request

 

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[Mike]

Here's some Sunday morning testing trivia.  I was surprised how slow everything was.

All testing was done on a 12F1840, since it is software selectable up to 32MHz.

[Rob CJ]

Hi Mike,

Some questions. What does PLL HW/SW mean and what does undefined mean?

The speed also depends on the speed of I2C device. If things go too fast, it might apply clock stretching to slow down the I2C host. Do you know if that is the case?

And would or high speeds I2C hardware be an option?

Kind regards,

Rob

---

Van: 'Mike' via jallib <jal...@googlegroups.com>

Verzonden: zondag 1 maart 2026 16:20

To view this discussion visit https://groups.google.com/d/msgid/jallib/0eca8088-1242-4390-b996-b5169a4b25a2n%40googlegroups.com.

[Mike]

Hi Rob,

The PIC that I used, the 12F1840, has an on-chip Phased Locked Loop and it can be enabled in the Configuration Word (what I called the Hardware setting) or by setting the appropriate bit in the OSCCON register (what I called the Software setting).  I tested both ways in case there was some silicon bug.

The I2C device that I used is a 128x32 OLED display, which I've previously used with a different microcontroller (not PIC), and running the I2C clock at more than 20MHz.

The 12F1840 does indeed have hardware I2C functionality, but I was deliberately testing the I2C Software library to see if "speed=255" was feasible at reasonable PIC oscillator speeds.

Regards,

Mike

[Mike]

Oh, and "undefined" referred to the speed setting not being one of the valid options, i.e. not 4, 10, or 255.

[Rob CJ]

Hi Mike,

OK. If you use any other values than 4, 10 or 255, the library uses 100 kHz (same as 1).

Kind regards,

Rob

---

Van: 'Mike' via jallib <jal...@googlegroups.com>

Verzonden: maandag 2 maart 2026 21:17

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