Calibre UK UCA93 Bus Capacitance Limitations/Cable Choice, Variable Voltage Bus Power Supply

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CALIBRE

IO 1 is a 5V TTL input and can only be used on 5V tolerant systems.

Pin

Function

1

NC – DO NOT CONNECT

2

IO 0

3

IO 1

4

0V

1.6.Bus Capacitance Limitations/Cable Choice

The maximum allowable capacitance on the I2C bus in normal mode depends on the value of the SCL and SDA master pull-ups, but never exceeds 400pF. Refer to Phillips Technical Handbook Book 4 Parts 12a and 12b for further details. Care should be taken in choosing a length and type of interconnecting cable, which will not exceed this limit.

For most systems with a distance of a few metres between the I2C Communications Adapter and the target system, screened cable is NOT recommended, as it is likely to introduce too much capacitance. However, the EMC performance of an unscreened cable is always potentially poorer than a screened one. The Adapter's EMC performance even with an unscreened cable is good - but this may not be true of the target system! If you are in any doubt at to the best way to connect up your system with EMC in mind please contact your supplier or Calibre for advice.

1.7.Variable Voltage Bus Power Supply

Pin 7 on the “D” connector is connected to the variable bus voltage power rail. Power for external circuitry can be drawn from here, but care should be taken never to short it to 0V or to exceed 250mA loading. It is short circuit and overload protected by a self-resetting thermal fuse but prolonged shorting could cause the UCA93 to generate an excessive amount of heat.

The bus voltage is set via software, in the range 2V to 5V.

NOTE that if a bus voltage greater 4.2V is selected the output will be 5V.

Issue 1.0

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01/07/03

 

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Contents Calibre Calibre Contents General Introduction Connecting the Adapter to your SystemPacking List Bus Termination and ProtectionBus Capacitance Limitations/Cable Choice Variable Voltage Bus Power SupplyIntroduction Installing the AdapterLibraries for Programming in Microsoft Windows Environments Function Prototypes Calibre Int ownaddress Int SlaveBlockTimeoutInt ClockSpeed Int BusVoltageSendAddress Int DataByteInt I2CData NoneInt I2Cstatus Using the AdapterInt NoTries Int NoBytesToSendInt DataVal Returns an unused integerInt NoBytesToTransmit Int TimeoutInt RdData Int NoBytesToReceive Int PullupVoltage Int Int IOStateSendAddressNoStatus WriteByteNoStatus Stop Real-Time Bus MonitorAppendix a I2C Communications Adapter Status Codes Bit 4 The BER Bus Error BitBit 7 MSB The old PIN Bit Bit 5 The old STS BitPolling the Status Register and how to avoid it USB Bus CharacteristicsBlock Functions Block Write FunctionSlave Receiver Function Slave Transmitter FunctionCalibre Question Get corrupted transfers why is this? When the the Most Commonly Asked I2C QuestionsGeneral Questions Question Do you have software to talk to my........?
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