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I will communicate with a device via SMBus. I use PIC18F26K83 for this. In SMBus spec it says clock minimum clock frequency is 10 kHz and maximum clock frequency is 100 kHz. Would it be a risk to use 100 kHz clock frequency since it is the boundary and max limit? Or is it safer to go with 75 kHz for example?

I will be using multiplexer and communicating with 3 smart batteries. Reading their SOC and send these data with UART to another PIC. Cable length from batteries to PIC will not be more than 1 meter long. I am planning to make MCU clock also 100 kHz.

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  • \$\begingroup\$ Operating at \$100\:\text{kHz}\$ is usually okay. Of course, details matter. But generally, it's not risky. We'd need more details about the context and specific details to offer more, I think. \$\endgroup\$ – jonk Mar 27 '19 at 7:06
  • \$\begingroup\$ Okay so I will be using multiplexer and communicating with 3 smart batteries. Reading their SOC and send these data with UART to another PIC. Cable length from batteries to PIC will not be more than 1 meter long. I am planning to make MCU clock also 100 kHz. \$\endgroup\$ – Günkut Ağabeyoğlu Mar 27 '19 at 7:19
  • \$\begingroup\$ Cable capacitance is a considerable issue with I2C, SMBus, etc.. If you are connecting the devices with a 1m long cable you should mention that on your question and not on the comments.. \$\endgroup\$ – Wesley Lee Mar 27 '19 at 7:24
  • \$\begingroup\$ from my understanding, generally 100KHz is defacto standard for most i2c chips and it would work with it without problems (or actually designed to work with it)?. \$\endgroup\$ – Hasan alattar Mar 27 '19 at 7:31
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If I read the Wikipedia page about SMBus I read that:

SMBus is derived from I²C

and

SMBus clock is defined from 10–100 kHz while I²C can be 0–100 kHz, 0–400 kHz, 0–1 MHz and 0–3.4 MHz, depending on the mode.

So it is simply a matter of definition that the SMBus clock should be 10 to 100 kHz.

It does not mean that a 1 Hz SMBus would not work. If you made your SMBus circuit such that it would work at 1 Hz, then it would. But then it does not meet the official SMBus specification so it would not be correct to call it an SMBus. But like I²C, it can work.

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