Port configuration issues when C8051F340 is connected to FM24C04

I originally wanted to use the SMBus port of the microcontroller, but the official example used several timers, and my small project also needs a lot of timers.

The timer resources are not enough. So I just use the IO port to simulate the I2C timing to operate the FM24C04. The project is not strict on time.

carve. 

Therefore, the question that this article will introduce arises:

When drawing the schematic diagram, the SDA/SCL port of SMBus (corresponding to P0_0/P0_1) has been connected to the SDA and SCL of FM24C04.

So according to the normal operation, I enabled SMB0E of XBR0 and connected it to the port. Then I set the corresponding IO ports P0_0 and P0_1 to open drain.

Road, it should be OK, right? Actually not, the data read during operation is always 0xFF, it may be high impedance state.

I checked the read and write operation codes and found no problems. I also couldn't change the timing by increasing or decreasing the delay. So I suspected that there was something wrong with the crossbar switch. 

After thinking about it, I thought, since I am using analog timing, why should I set it to open drain? Why should I configure the port to SMBus? Isn't push-pull also

Is it possible? So as shown below, set SMB0E to zero. Burn, debug and run, read and write are OK. In addition, the corresponding IO port settings

Open drain or push-pull can operate normally.