Datasheet

DESCRIPTORDATAMODIFICATION
ExternalROMDescriptor(PCM2704/6)
9
DT
CK S
Start Condition
1−7 8 1−8 9 1−8 9 9 P
Stop Condition
Device Address ACK DATA ACK DATA ACK NACKR/W
R/W: Read Operation if 1; Otherwise, Write Operation
ACK: Acknowledgment of a Byte if 0
DATA: 8 Bits (Byte)
NACK: Not Acknowledgment if 1
T0049-02
PCM2704, ,PCM2705
PCM2706,PCM2707
www.ti.com .......................................................................................................................................................SLES081F–JUNE2003–REVISEDJANUARY2009
ThedescriptordatacanbemodifiedthroughI
2
CportbyexternalROM(PCM2704/6)orthroughourSPIportby
anSPIhostsuchasanMCU(PCM2705/7)underaparticularconditionofPSELpinandHOSTpin.Acondition
ofPSELpin=HighandHOSTpin=Highisneededtomodifythedescriptordata,andD+pull-upmustnotbe
activatedbeforecompletionofprogrammingthedescriptordatathroughexternalROMorSPIport.The
descriptordatahavetobesentfromexternalROMtoPCM2704/6ororfromSPIhosttoPCM2705/7inLSBfirst
withspecifiedbyteorder.Also,thecontentofthepowerattributeandmaxpowermustbeconsistentwithPSEL
settingandpowerusagefromUSBVBUSofactualapplication.Therefore,thedescriptordatamodificationin
self-poweredconfiguration(PSEL=Low)isnotsupported.
ThePCM2704/6supportsanexternalROMinterfacetooverrideinternaldescriptors.Pin3(forPCM2704)/pin15
(forPCM2706)isassignedasDT(serialdata)andpin2(forPCM2704)/pin14(forPCM2706)isassignedasCK
(serialclock)oftheI
2
CinterfacewhenusingtheexternalROMdescriptor.Descriptordataistransferredfromthe
externalROMtothePCM2704/6throughtheI
2
Cinterfacethefirsttimewhenthedeviceactivatesafterpower-on
reset.BeforecompletingareadoftheexternalROM,thePCM2704/6replieswithNACKforanyUSBcommand
requestfromthehosttothedeviceitself.Thedescriptordata,whichcanbeinexternalROM,areasfollows.
StringdescriptorsmustbedescribedinANSIASCIIcode(1byteforeachcharacter).Stringdescriptorsare
convertedautomaticallytounicodestringsfortransmissiontothehost.ThedeviceaddressoftheexternalROM
isfixedas0xA0.Thedatamustbestoredfromaddress0x00andmustconsistof57bytes,asdescribedinthe
followingitems.ThedatabitsmustbesentfromLSBtoMSBontheI
2
Cbus.Thismeansthateachbyteofdata
mustbestoredwithitsbitsinreverseorder.ReadoperationisperformedatafrequencyofXTI/384
(approximately30kHz).Thecontentofpowerattributeandmaxpowermustbeconsistentwithactualapplication
circuitconfiguration(PSELsettingandactualpowerusagefromVBUSofUSBconnector);otherwise,itmay
causeimproperorunexpectedPCM2704/6operation.
•VendorID(2bytes)
•ProductID(2bytes)
•Productstring(16bytesinANSIASCIIcode)
•Vendorstring(32bytesinANSIASCIIcode)
•Powerattribute(1byte)
•Maxpower(1byte)
•AuxiliaryHIDusageIDinreportdescriptor(3bytes)
MMMSSMSMSMM
SDeviceaddressR/WACKDATAACKDATAACK...NACKP
Figure25.ExternalROMReadOperation
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ProductFolderLink(s):PCM2704PCM2705PCM2706PCM2707
PCM2704 and PCM2705
Not Recommended For New Designs