Datasheet

Data From
Shift Register
Write Configuration
Pulse
Write Pulse
Read Pulse
Write Polarity Pulse
Polarity
Inversion
Register
Input
Port
Register
Output
Port
Register
Configuration
Register
V
CCP
GND
Input Port
Register Data
Polarity
Register Data
ESD Protection Diode
P0 to P7
Output Port
Register Data
To INT
Q1
Q2
D
FF
C
K
Q
Q
D
FF
C
K
Q
Q
D
FF
C
K
Q
Q
D
FF
C
K
Q
Q
Data From
Shift Register
Data From
Shift Register
I/OPort
I
2
CInterface
TCA6408A
SCPS192C–APRIL2009–REVISEDJULY2009............................................................................................................................................................. www.ti.com
SimplifiedSchematicofP0toP7
A.Onpoweruporreset,allregistersreturntodefaultvalues.
WhenanI/Oisconfiguredasaninput,FETsQ1andQ2areoff,whichcreatesahigh-impedanceinput.The
inputvoltagemayberaisedaboveV
CC
toamaximumof5.5V.
IftheI/Oisconfiguredasanoutput,Q1orQ2isenableddependingonthestateoftheOutputPortRegister.In
thiscase,therearelowimpedancepathsbetweentheI/OpinandeitherV
CC
orGND.Theexternalvoltage
appliedtothisI/Opinshouldnotexceedtherecommendedlevelsforproperoperation.
ThebidirectionalI
2
Cbusconsistsoftheserialclock(SCL)andserialdata(SDA)lines.Bothlinesmustbe
connectedtoapositivesupplythroughapullupresistorwhenconnectedtotheoutputstagesofadevice.Data
transfermaybeinitiatedonlywhenthebusisnotbusy.
I
2
CcommunicationwiththisdeviceisinitiatedbyamastersendingaStartcondition,ahigh-to-lowtransitionon
theSDAinput/output,whiletheSCLinputishigh(seeFigure1).AftertheStartcondition,thedeviceaddress
byteissent,mostsignificantbit(MSB)first,includingthedatadirectionbit(R/W).
Afterreceivingthevalidaddressbyte,thisdevicerespondswithanacknowledge(ACK),alowontheSDA
input/outputduringthehighoftheACK-relatedclockpulse.Theaddress(ADDR)inputoftheslavedevicemust
notbechangedbetweentheStartandtheStopconditions.
OntheI
2
Cbus,onlyonedatabitistransferredduringeachclockpulse.ThedataontheSDAlinemustremain
stableduringthehighpulseoftheclockperiod,aschangesinthedatalineatthistimeareinterpretedascontrol
commands(StartorStop)(seeFigure2).
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