DS90UB928Q-Q1: How to set I2C speed?

Youhei Miyaoka

Hello team,

My customer understand 0x26 and 0x27 is I2C speed setting register. But they are not sure what exact value makes their target frequency. They want to set I2C 100kbps, currently setting value is 0x64 and its result is 80kbps, can you share correct setting please?

Regards,

Youhei MIYAOKA

2 months ago

0 Miguel Bolante 2 months ago

TI__Mastermind 24835 points

Hi Miyaoka-san,

Thanks for your inquiry, you can reference this table below (from latest FPD-Link guidance) and we can go through the values together

			Min/Max	Unit
f_SCL	SCL Clock Frequency	Standard-mode	100 (Max)	kHz
		Fast-mode	400 (Max)	kHz
		Fast-mode Plus	1 (Max)	MHz
		High-speed-mode	3.4 (Max)	MHz
t_LOW	SCL Low Period	Standard-mode	4.7 (Min)	μs
		Fast-mode	1.3 (Min)	μs
		Fast-mode Plus	0.5 (Min)	μs
		High-speed-mode	0.16 (Min)	μs
t_HIGH	SCL High Period	Standard-mode	4 (Min)	μs
		Fast-mode	0.6 (Min)	μs
		Fast-mode Plus	0.26 (Min)	μs
		High-speed-mode	0.06 (Min)	μs

Apologies for the formatting, E2E is currently having file upload issues. So they want to use I2C 100kHz I am assuming, Standard-mode.

SCL Low period shall be set to 4.7μs, SCL High period shall be set to 4μs

Now for the registers:

0x27 SCL Low Time = Units of 50 ns for nominal oscillator frequency

4700ns / 50ns = decicmal 94 = 0x5E

0x27 = 0x5E

0x26 SCL High time = Units of 50 ns for nominal oscillator frequency

4000ns / 50ns = decimal 80 = 0x50

0x26 = 0x50

As a reminder, these fields configure the SCL and SDA only for when the DES is the controller of the local I2C bus, not FPD-Link speeds.

Please let me know if you have any further questions!

Best,

Miguel

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DS90UB928Q-Q1: How to set I2C speed?