MPC5xxxのトピックRe: I2C time frequency configure

I2C time frequency configure

huqiang — Thu, 02 Jun 2016 14:44:47 GMT

Hi everybody!

When configing the I2C module in MPC5748G, there is something puzzle me about the frequency of the SCL for I2C bus. For example, IBFD=0x20

what's the unit of the number 160, 17, 78, 81? stands for how long time?

What should I do if I want to have a 400KHz I2C bus?

PetrS — Fri, 03 Jun 2016 04:53:46 GMT

Hi,

The I2C module is clocked from F40 clock group (max 40MHz). The IBFD[IBC] field is used to divide this module clock to give desired bit rate.

If you want for example 100kHz I2C bus then simply calculate divider as

divider = F40 / bit rate = 40MHz / 100kHz = 400.

Now from Table 44-11 find closest SCL divider and use respective IBC value.

So you can select SCL divider = 416 and IBFD = 0x96.

The SCL Divider, SDA Hold and SCL Hold (start/stop) values represent time duration in number of module clock.

For 400kHz I2C bus, assuming max 40MHz module clock, you get divider = 100, then select IBFD = 0x16.

BR, Petr

huqiang — Fri, 03 Jun 2016 12:52:18 GMT

Hi, Petr

Thank you very much for your help! I will do it later.

Best Regards,

Qiang