I2C frequency accuracy

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by guillaumeL on Tue Nov 20 05:37:47 MST 2012

  I'm developing an application using I2C interface of the LPC1769. All is working fine but it seems the I2C SCL frequency is not accurate. For example, when I want this frequency at 100kHz it is OK but if I set 400kHz the frequency is only 350 kHz.

  I use the PLL0 with Main oscillator @ 12MHz as input. The setting of the PLL is LPC_SC->PLL0CFG = 0x10018; (N= 2 & M = 25). Fcco is 300 MHz and I set LPC_SC->CCLKCFG = 0x02; to get 100MHz as system clock.

  I2C clk is equal to system clock.

  Do you know where this frequency "error" can come from?