Datasheet

DeviceAddress
0 1 0 0 A1A2 A0
Slave Address
R/W
Fixed Programmable
ControlRegisterandCommandByte
0 0 0 B2 B1 B00
0
PCA9555
SCPS131E–AUGUST2005–REVISEDMAY2008......................................................................................................................................................... www.ti.com
Figure4showstheaddressbyteofthePCA9555.
Figure4.PCA9555Address
AddressReference
INPUTS
I
2
CBUSSLAVEADDRESS
A2A1A0
LLL32(decimal),20(hexadecimal)
LLH33(decimal),21(hexadecimal)
LHL34(decimal),22(hexadecimal)
LHH35(decimal),23(hexadecimal)
HLL36(decimal),24(hexadecimal)
HLH37(decimal),25(hexadecimal)
HHL38(decimal),26(hexadecimal)
HHH39(decimal),27(hexadecimal)
Thelastbitoftheslaveaddressdefinestheoperation(readorwrite)tobeperformed.Ahigh(1)selectsaread
operation,whilealow(0)selectsawriteoperation.
Followingthesuccessfulacknowledgmentoftheaddressbyte,thebusmastersendsacommandbytethatis
storedinthecontrolregisterinthePCA9555.Threebitsofthisdatabytestatetheoperation(readorwrite)and
theinternalregister(input,output,polarityinversion,orconfiguration)thatwillbeaffected.Thisregistercanbe
writtenorreadthroughtheI
2
Cbus.Thecommandbyteissentonlyduringawritetransmission.
Onceacommandbytehasbeensent,theregisterthatwasaddressedcontinuestobeaccessedbyreadsuntila
newcommandbytehasbeensent.
Figure5.ControlRegisterBits
CommandByte
CONTROLREGISTERBITS
COMMANDPOWER-UP
REGISTERPROTOCOL
BYTE(HEX)DEFAULT
B2B1B0
0000x00InputPort0Readbytexxxxxxxx
0010x01InputPort1Readbytexxxxxxxx
0100x02OutputPort0Read/writebyte11111111
0110x03OutputPort1Read/writebyte11111111
1000x04PolarityInversionPort0Read/writebyte00000000
1010x05PolarityInversionPort1Read/writebyte00000000
1100x06ConfigurationPort0Read/writebyte11111111
1110x07ConfigurationPort1Read/writebyte11111111
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Not Recommended for New Designs