nRF54 TWIM/I2C clock pin assignment

[pejetro]

Hello,

As I understand, the nRF54L15  have pins dedicated for clock functionality.

They are marked red in figure 165 ( page 796) of the preliminary datasheet, rev. 0.8.

Table 72 (page 795) also state that for the SCL signal of TWIM, clock pin is required.

Does this mean that the SCL signal must be assigned to one of these "dedicated" clock pins?

Or could any pin be used?

BR Per

[khelmutlord]

Hello,

I created this (unofficial) pin planner application: https://hlord2000.github.io/

The SCL pin does indeed need to be on a clock pin with some further restrictions depending on which GPIO peripheral you intend to use.

One other caveat: please be sure to only use GPIO of a single peripheral. I.e. if you use TWIM20 w/ SCL on P1.03, use any pin on P1 for SDA.

Thanks,

Helmut Lord

[pejetro]

Thank you very much for your quick answer Helmut.

This was very helpful, and your pin-application was brilliant.

In our first project where we used nRF54 we had an I2C communication towards a temperature sensor,

and we didn't use the correct clock-pin for the SCL-signal, but apparently it worked.

What is the difference between these clock-pins and other pins? Driving capabilities? speed? ??

For that project we had I2C at port-0, and then it must the peripheral-block TWIM30, right?

However, now we have a new project with several serial communication channels.

I have included a schematic showing the pin-assignment. Could you please have a look and see if this looks ok?

There are 2 channels for I2C (P1.02/P1.03 and P1.07/P1-08), and 2 channels for SPI.

The SPI channel with signal names MOSI, MISO and CLK have communication towards 2 devices (Ethernet and WiFi).

The associated chip-select signals are: ETH_CSn and WiFI_CSn

The other SPI channel (ASPECT_MOSI, ASPECT_MISO and ASPECT_CLK) is special, because it shall be 

possible to reconfigure this SPI channel to be a UART, i.e. to switch from MOSI/MISO to TXD/RXD.

Do you see any problem with this Helmut?

BR PerJe455 Pin assignment.pdf

[Edvin]

Hello Per,

Indeed, I liked your pin-application, Helmut! I haven't seen it before. 

pejetro said:

What is the difference between these clock-pins and other pins? Driving capabilities? speed? ??

I don't know the details down to transistor level, but it is related to the traces inside the chip. They are shorter, and hence have more drive strength, but they are also routed further away from sensitive components, such as the radio. 

pejetro said:

and we didn't use the correct clock-pin for the SCL-signal, but apparently it worked

Some things may physically work, but you risk seeing side effects, e.g. in radio sensitivity. So I really recommend that you use the recommended clock pins even though it seemingly works with other pins.

pejetro said:

There are 2 channels for I2C (P1.02/P1.03 and P1.07/P1-08), and 2 channels for SPI.

P1.03 is a clock pin used for I2C SCL, so that is fine. The same goes for P1.08.

Also your SPI CLK pin is a clock pin (1.04), and the same for ASPECT_CLK (1.12).

So from a pin selection perspective this looks good. I am not sure about the pullups and capacitors. (not saying it is not good, but outside my field of knowledge), but if you want to I can have a colleague have a look. Let me know. But please note that we are very short staffed on HW experts this week and the next. So I can't guarantee a response on that part before the week after next week.

But at the same time, if you want someone to look over your HW layout, you may want to open a new ticket, and upload your schematics (PCB files) for a proper review. You may want to create a private ticket for this. 

But the pin selection for your SPIs and TWIs looks good to me!

Best regards,

Edvin