I2C speed...

[Piotr Wyderski]

Don wrote:

> Never mind. Your desire to use fast mode is clearly stated above.

The slowest slave on the bus is specified to support only fast mode, so
I have no choice but to comply.

Best regards, Piotr

 

[Jan Panteltje]

On a sunny day (Sun, 30 Jul 2023 20:19:27 +0200) it happened Piotr Wyderski
<bombald@protonmail.com> wrote in <ua69jf$3m59o$1@portraits.wsisiz.edu.pl>:

Don wrote:

Never mind. Your desire to use fast mode is clearly stated above.

The slowest slave on the bus is specified to support only fast mode, so
I have no choice but to comply.

Best regards, Piotr

How does that work?
The advantage of i2c is that you can interrupt it.
this allows it to be used in a multi-tasking system where it can be interrupted all the time.
No minimal speed specified.

 

[Piotr Wyderski]

Jan Panteltje wrote:

> How does that work?

It\'s a regular single master I2C bus driven from a PicoBlaze. The
slowest device is fast mode, so all of them need to be fast mode.

> The advantage of i2c is that you can interrupt it.

I hate I2C, too many things can go wrong. But there are no SPI variants
of the chips I need, so I have no choice.

> No minimal speed specified.

Yup, I2C is all about the SCL/SDA edges.

Best regards, Piotr

 

[Jan Panteltje]

On a sunny day (Mon, 31 Jul 2023 07:58:51 +0200) it happened Piotr Wyderski
<bombald@protonmail.com> wrote in <ua7iir$3mtta$1@portraits.wsisiz.edu.pl>:

Jan Panteltje wrote:

How does that work?

It\'s a regular single master I2C bus driven from a PicoBlaze. The
slowest device is fast mode, so all of them need to be fast mode.

Still wonder, you can drive any device slower than fastmode, never seen one specified that MUST use fast mode.
Or are you sending / receiving data at high speed that needs it?

The advantage of i2c is that you can interrupt it.

I hate I2C, too many things can go wrong. But there are no SPI variants
of the chips I need, so I have no choice.

I like it, even did an external i2c network in an office building showing data on displays...
Used differential drive and interface chips...
Hundreds of meters...

Not sure if I used SDA pulldown to confirm....
Early eighties.

No minimal speed specified.

Yup, I2C is all about the SCL/SDA edges.

Indeed.

 

[Piotr Wyderski]

Jan Panteltje wrote:

Still wonder, you can drive any device slower than fastmode, never seen one specified that MUST use fast mode.
Or are you sending / receiving data at high speed that needs it?

Oh, sure, there probably is none. I want to complete the transfers as
fast as possible. \"Fast mode\" is slow enough not to consider going down
to 100kHz. It\'s not about the bus frequency itself, but about the query
delay it introduces.

I like it, even did an external i2c network in an office building showing data on displays...
Used differential drive and interface chips...
Hundreds of meters...

I have 125MHz LVDS for interfacing the external world. This one is an
entirely on-board issue.

Best regards, Piotr

 

[Lasse Langwadt Christensen]

mandag den 31. juli 2023 kl. 06.45.27 UTC+2 skrev Jan Panteltje:

On a sunny day (Sun, 30 Jul 2023 20:19:27 +0200) it happened Piotr Wyderski
bom...@protonmail.com> wrote in <ua69jf$3m59o$1...@portraits.wsisiz.edu.pl>:
Don wrote:

Never mind. Your desire to use fast mode is clearly stated above.

The slowest slave on the bus is specified to support only fast mode, so
I have no choice but to comply.

Best regards, Piotr
How does that work?
The advantage of i2c is that you can interrupt it.
this allows it to be used in a multi-tasking system where it can be interrupted all the time.
No minimal speed specified.

except when it is actually SMBus like many devices on a motherboard, it has a timeout
to resolve the lockups I2C is prone to if you look at it the wrong way

 

[John Walliker]

On Monday, 31 July 2023 at 15:23:39 UTC+1, Lasse Langwadt Christensen wrote:

mandag den 31. juli 2023 kl. 06.45.27 UTC+2 skrev Jan Panteltje:
On a sunny day (Sun, 30 Jul 2023 20:19:27 +0200) it happened Piotr Wyderski
bom...@protonmail.com> wrote in <ua69jf$3m59o$1...@portraits.wsisiz.edu.pl>:
Don wrote:

Never mind. Your desire to use fast mode is clearly stated above.

The slowest slave on the bus is specified to support only fast mode, so
I have no choice but to comply.

Best regards, Piotr
How does that work?
The advantage of i2c is that you can interrupt it.
this allows it to be used in a multi-tasking system where it can be interrupted all the time.
No minimal speed specified.
except when it is actually SMBus like many devices on a motherboard, it has a timeout
to resolve the lockups I2C is prone to if you look at it the wrong way

An essential component of an i2c controller is a power switch for all the slaves.
(Yes, I do know about clocking errors out, but it doesn\'t work EVERY time.)

I have regularly used i2c over 10m cables at 100kHz and even got it through EMC immunity
testing for CE marking over unshielded cables, but it does help to have a linear bus structure
and to provide some RC damping at one end at least.
John