Philips MIIC-201D/U manual

3 Hardware Configuration

3.1Pull-up Resistors

I2C Bus systems are based on open-collector technology requiring pull-up devices on each signal wire. These pull-up devices usually take the form of pull-up resistors connected to bus power.

The I2C adapter includes a slide switch used to enable or disable internal +5VDC I2C Bus 1.8K ohm pull-up resistors attached to the SCL, SDA, and /INT lines. Every I2C Bus system must have at least one pull-up on the signal lines. Use this switch to configure the pull-up resistors for your system.

3.2Connecting to a 3.3 Volt Target System

If you are connecting the I2C adapter to a 3.3 volt target system, you should follow these steps BEFORE applying power:

•Shut off the I2C adapter’s internal pull-ups (See Pull-up Resistor section). Use external pull-ups to the target system’s 3.3V power. These pull-ups may already be present in the target system.

•Disconnect the I2C connector +5V wire from the target system. The I2C adapter will be powered from its own +5V power supply, and the target system will be powered by its own 3.3V power supply.

The I2C adapter is a 5-volt device. Any signal above 3.3V on the SCL, SDA, and /INT lines is high enough for the adapter to see a Logical 1.

3.3Connecting to an SMBus Target System

If you are connecting the I2C adapter to a SMBus target system, you should follow these steps BEFORE applying power:

•Shut off the I2C adapter’s internal pull-ups (See Pull-up Resistor section).

•Use external SMBus rated (appoximately15k ohms) pull-up resistors. These pull-ups may already be present in the target system.

•Visit our I2C versus SMBus FAQ page (www.mcc-us.com/I2CSMBusFAQ.htm).

•See the SMBus Specification for additional details.

Special Note for SMBus Users: MCC’s I2C adapters are designed to be I2C Bus

6