Note About I2C Devices on Rev F I2C Port

[JonnyMac]

The Rev F version of the HC-8+ brings out a buffered I2C port to enable myriad expansion capabilities. This I2C buss is used by the Propeller's EEPROM which can lead to issues when attempting to reprogram the Propeller (store to EE). Some devices cannot cope with the I2C speeds used by the Propeller when writing to EEPROM, hence may interfere with the programming process. I saw this today when using a Newhaven I2C LCD. Checking the spec sheet it has a maximum I2C speed of 100kHz, about 1/4 the speed used by the Propeller when reprogramming the EEPROM.

All this is to say that you may need to disconnect external I2C devices when reprogramming. Once the code is safely in the Propeller's EEPROM you can power down and re-connect the external devices.

[bsnut]

Once the code is safely in the Propeller's EEPROM you can power down and re-connect the external devices.

I was thinking about a electronic disconnect but, this would use one I/O pin from the HC-8's brain, which is good in a permanent installation. Which this means you have to have this pin go high before talking on the I2C bus, basically you are doing a normally open circuit. I think it would save time from disconnecting from the I2C header every time download Propeller's EEPROM.

Do you think this is a good idea or just waste of time? 

[JonnyMac]

I tend to keep things simple, and would rather have an output available to connect working devices. Remember, this situation comes up only when low-speed I2C devices are connected to the I2C header. I have used a couple other devices that created no problem at all. In this case, it's a multi-mode display (serial, SPI, I2C) and the I2C spec is slower than the Propeller programming speed.

[JonnyMac]

UPDATE!

Slow I2C devices cannot be used on the HC-8+ I2C port. Period. Why? Because they interfere with the Propeller boot process. I didn't think about this the other day but just encountered it

Tip: Multi-mode (Serial, SPI, I2C) devices probably cannot be attached to the I2C port because they don't operate at 400kHz I2C speeds. Look for devices that have known I2C chips onboard, not processors handling the I2C ,