2.3.2GigabitMediaIndependentInterface(GMII)Connections
MTCLK
MTXD[7−0]
MTXEN
MCOL
MCRS
MRCLK
MRXD[7−0]
MRXDV
MRXER
MDCLK
MDIO
Physical
layer
device
(PHY)
System
core
Transformer
2.5 MHz,
25 MHz,
RJ−45
EMACMDIO
GMTCLK
or 125 MHz
RFTCLK
Architecture
Figure3showsadevicewithintegratedEMACandMDIOinterfacedviaaGMIIconnection.Thisinterface
isavailablein10Mbps,100Mbps,and1000Mbpsmodes.
TheGMIIinterfacesupports10/100/1000Mbpsmodes.Onlyfull-duplexmodeisavailablein1000Mbps
mode.In10/100Mbpsmodes,theGMIIinterfaceactslikeanMIIinterfaceandonlythelower4bitsof
dataaretransferredforeachofthedatabuses.TheindividualEMACandMDIOsignalsfortheGMII
interfacearesummarizedinFigure3.
Figure3.EthernetConfiguration—GMIIConnections
Table2.EMACandMDIOSignalsforGMIIInterface
SignalTypeDescription
MTCLKITransmitclock(MTCLK).Thetransmitclockisacontinuousclockthatprovidesthetimingreference
fortransmitoperationsin10/100Mbpsmode.TheMTXDandMTXENsignalsaretiedtothisclock
whenin10/100Mbpsmode.TheclockisgeneratedbythePHYandis2.5MHZat10Mbps
operation,and25MHZat100Mbpsoperation.
GMTCLKOGMIIsourcesynchronoustransmitclock(GMTCLK).Thisclockisusedin1000Mbpsmodeonly,
providingacontinuous125MHZfrequencyfortransmitoperations.TheMTXDandMTXENsignals
aretiedtothisclockwheninGigabitmode.TheclockisgeneratedbytheEMACandis125MHZ.
RFTCLKIReferencetransmitclock(RFTCLK).Thereferencetransmitclockisacontinuousclockthatprovides
thetimingreferencefortransmitoperationsin1000Mbpsmode.This125-MHZclockisgenerated
bythePHY.
MTXD[7-0]OTransmitdata(MTXD).Thetransmitdatapinsareacollectionof8datasignalscomprising8bitsof
data.MTDX0istheleast-significantbit(LSB).ThesignalsaresynchronizedbyMTCLKin10/100
Mbpsmode,andbyGMTCLKinGigabitmode,andvalidonlywhenMTXENisasserted.
MTXENOTransmitenable(MTXEN).ThetransmitenablesignalindicatesthattheMTXDpinsaregenerating
nibbledataforusebythePHY.ItisdrivensynchronouslytoMTCLKin10/100Mbpsmode,andto
GMTCLKinGigabitmode.
MCOLICollisiondetected(MCOL).TheMCOLpinisassertedbythePHYwhenitdetectsacollisiononthe
network.Itremainsassertedwhilethecollisionconditionpersists.Thissignalisnotnecessarily
synchronoustoMTCLKnorMRCLK.Thispinisusedinhalf-duplexoperationonly.
SPRUEQ6–December2007EthernetMediaAccessController(EMAC)/ManagementDataInput/Output(MDIO)17
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