Datasheet

Data From
Shift Register
Data From
Shift Register
Write Configuration
Pulse
Write Pulse
Read Pulse
Write Polarity
Pulse
Data From
Shift Register
Output Port
Register
Configuration
Register
Input Port
Register
Polarity
Inversion
Register
Polarity
Register Data
Input Port
Register Data
GND
P0 to P7
V
C
C
Output Port
Register Data
Q1
Q2
D
C
K
FF
Q
Q
D
C
K
FF
Q
Q
D
C
K
FF
Q
Q
D
C
K
FF
Q
Q
INT
100 kW
I/OPort
I
2
CInterface
PCA9554
SCPS128B–JULY2006–REVISEDAUGUST2008........................................................................................................................................................ www.ti.com
SimplifiedSchematicofP0toP7
A.Atpower-onreset,allregistersreturntodefaultvalues.
WhenanI/Oisconfiguredasaninput,FETsQ1andQ2areoff,whichcreatesahigh-impedanceinputwitha
weakpullup(100kΩtyp)toV
CC
.TheinputvoltagemayberaisedaboveV
CC
toamaximumof5.5V.
IftheI/Oisconfiguredasanoutput,Q1orQ2isenabled,dependingonthestateoftheoutputportregister.In
thiscase,therearelow-impedancepathsbetweentheI/OpinandeitherV
CC
orGND.Theexternalvoltage
appliedtothisI/Opinshouldnotexceedtherecommendedlevelsforproperoperation.
ThebidirectionalI
2
Cbusconsistsoftheserialclock(SCL)andserialdata(SDA)lines.Bothlinesmustbe
connectedtoapositivesupplythroughapullupresistorwhenconnectedtotheoutputstagesofadevice.Data
transfermaybeinitiatedonlywhenthebusisnotbusy.
I
2
Ccommunicationwiththisdeviceisinitiatedbyamastersendingastartcondition,ahigh-to-lowtransitionon
theSDAinput/outputwhiletheSCLinputishigh(seeFigure1).Afterthestartcondition,thedeviceaddressbyte
issent,MSBfirst,includingthedatadirectionbit(R/W).
Afterreceivingthevalidaddressbyte,thisdevicerespondswithanacknowledge(ACK),alowontheSDA
input/outputduringthehighoftheACK-relatedclockpulse.Theaddressinputs(A0–A2)oftheslavedevicemust
notbechangedbetweenthestartandthestopconditions.
OntheI
2
Cbus,onlyonedatabitistransferredduringeachclockpulse.ThedataontheSDAlinemustremain
stableduringthehighpulseoftheclockperiod,aschangesinthedatalineatthistimeareinterpretedascontrol
commands(startorstop)(seeFigure2).
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Not Recommended for New Designs