MSP430F6779A: MSP430F6779A I2C Clock Generation and Synchronization

Vasu Khwanyuen

Dear Ti Support,

I have question about I2C Clock Generation and Synchronization.

1. What happened when we setting FBitClock for I2C 400 kHz but FBRCLK is 1 Mhz (in the user guide FBitClock maximum is FBRCLK / 4)?.

2. Can the I2C be operated to sent and received data correctly in this setting (no.1)?.

Thank,

Vasu Khwanyuen

over 5 years ago

+1 Bruce McKenney over 5 years ago

Guru 102905 points

1) You can't set FBitClock directly, it is set using an integer divisor (BRW) from Fbrclk. So (e.g.) you can't get 400kHz using Fbrclk=1MHz, only 250/333/500.

2) Observed behavior with the eUSCI on the FR2 series was that if you set e.g. Fbrclk/3=333kHz the actual bus operates slower (maybe 200kHz? It's been a while.). I suspect this has to do with some combination of (a) microcode in the eUSCI device itself and (b) timing constraints from the I2C spec. It still works since the master is in charge of the clock.

https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/954529/msp430fr2311-i2c-clock-speed-too-slow

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MSP430F6779A: MSP430F6779A I2C Clock Generation and Synchronization