7
If you are connecting the I
2
C adapter to a 3.3 volt target system, you should follow
these steps BEFORE applying power:
• Shut off the iPort/USB 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 I
2
C Bus connector +5V wire from the target system. The
iPort/USB will be powered from the USB, and the target system will be powered
by its own 3.3V power supply.
The I
2
C adapter is a 5-volt device. Any signal at or above 3.3V on the SCL, SDA,
and /INT lines is high enough for the adapter to see a Logical 1.
3.3 Connecting to an SMBus Target System
If you are connecting the I
2
C adapter to a SMBus target system, you should follow
these steps BEFORE applying power:
• Shut off the iPort/USB 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 I
2
C versus SMBus FAQ page (www.mcc-us.com/I2CSMBusFAQ.htm).
• See the SMBus Specification for additional details.
Special Note for SMBus Users: MCC’s I
2
C adapters are designed to be I
2
C Bus
compatible, not SMBus compatible. Some features of the SMBus protocol not
supported include time-outs, device reset, and Packet Error Check byte processing.
The non-supported SMBus features may, or may not, permit the use of the I
2
C
adapter in your SMBus application. Consult the MCC FAQ web page and SMBus
Specification for details.
4 ESD (Electrostatic Discharge) Precautions
Electrostatic discharge is defined as the transfer of charge between bodies at
different electrical potentials. Electrostatic discharge can change the electrical
characteristics of a semiconductor device, degrading or destroying it. Electrostatic
discharge also may upset the normal operation of an electronic system, causing
equipment malfunction or failure.
When connecting the I
2
C adapter to a host computer and a target system, extreme
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