Datasheet

DeviceAddress
0 1 1
1
A1A2
A0
Slave Address
R/W
Fixed
Hardware
Selectable
ControlRegisterandCommandByte
0 0 0 0 B1 B000
PCA9554A
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Figure4showstheaddressbyteforthePCA9554A.
Figure4.PCA9554AAddress
AddressReference
INPUTS
I
2
CBUSSLAVEADDRESS
A2A1A0
LLL56(decimal),38(hexadecimal)
LLH57(decimal),39(hexadecimal)
LHL58(decimal),3A(hexadecimal)
LHH59(decimal),3B(hexadecimal)
HLL60(decimal),3C(hexadecimal)
HLH61(decimal),3D(hexadecimal)
HHL62(decimal),3E(hexadecimal)
HHH63(decimal),3F(hexadecimal)
Thelastbitoftheslaveaddressdefinestheoperation(readorwrite)tobeperformed.Whenitishigh(1),aread
isselected.Alow(0)selectsawriteoperation.
Followingthesuccessfulacknowledgmentoftheaddressbyte,thebusmastersendsacommandbytethatis
storedinthecontrolregisterinthePCA9554A.Twobitsofthiscommandbytestatetheoperation(readorwrite)
andtheinternalregister(input,output,polarityinversionorconfiguration)thatwillbeaffected.Thisregistercan
bewrittenorreadthroughtheI
2
Cbus.Thecommandbyteissentonlyduringawritetransmission.
Onceacommandbytehasbeensent,theregisterthatwasaddressedcontinuestobeaccessedbyreadsuntila
newcommandbytehasbeensent.
Figure5.ControlRegisterBits
CommandByte
CONTROLREGISTERBITS
COMMANDBYTEPOWER-UP
REGISTERPROTOCOL
(HEX)DEFAULT
B1B0
000x00InputPortReadbyteXXXXXXXX
010x01OutputPortRead/writebyte11111111
100x02PolarityInversionRead/writebyte00000000
110x03ConfigurationRead/writebyte11111111
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Not Recommended for New Designs