ICS1894-40
10BASE-T/100BASE-TX INTEGRATED PHYCEIVER WITH RMII INTERFACE
PHYCEIVER
RMII Signal Definition
The following table describes the RMII signals. Refer to RMII Specification for detailed information.
RMII Signal Name
Direction
Direction
Description
(with respect to PHY, (with respect to MAC)
ICS1894-40 signal)
REF_CLK
Input
Input or Output
Synchronous 50 MHz clock reference for
receive, transmit and control interface
TX_EN
TXD[1:0]
CRS_DV
RXD[1:0
RX_ER
Input
Input
Output
Transmit Enable
Output
Transmit Data [1:0]
Carrier Sense/Receive Data Valid
Receive Data [1:0]
Receive Error
Output
Output
Output
Input
Input
Input, or (not required)
follows the final di-bit. The data on RXD[1:0] is considered
valid once CRS_DV is asserted. However, since the
assertion of CRS_DV is asynchronous relative to
REF_CLK, the data on RXD[1:0] is "00" until proper receive
signal decoding takes place.
Reference Clock (REF_CLK)
REF_CLK is sourced by the MAC or system board. It is a
continuous 50MHz clock that provides the timing reference
for TX_EN, TXD[1:0], CRS_DV, RXD[1:0], and RX_ER.
Transmit Enable (TX_EN)
Receive Data [1:0] (RXD[1:0])
TX_EN indicates that the MAC is presenting di-bits on
TXD[1:0] for transmission. It is asserted synchronously with
the first nibble of the preamble and remains asserted while
all di-bits to be transmitted are presented on the RMII, and
is negated prior to the first REF_CLK following the final di-bit
of a frame. TX_EN transitions synchronously with respect to
REF_CLK.
RXD[1:0] transitions synchronously to REF_CLK. For each
clock period in which CRS_DV is asserted, RXD[1:0]
transfers two bits of recovered data from the PHY. RXD[1:0]
is "00" to indicate idle when CRS_DV is de-asserted. Values
other than “00” on RXD[1:0] while CRS_DV is de-asserted
are ignored by the MAC.
Receive Error (RX_ER)
Transmit Data [1:0] (TXD[1:0])
RX_ER is asserted for one or more REF_CLK periods to
indicate that an error (e.g. a coding error or any error that a
PHY is capable of detecting, and that may otherwise be
undetectable by the MAC sub-layer) was detected
somewhere in the frame presently being transferred from
the PHY. RX_ER transitions synchronously with respect to
REF_CLK. While CRS_DV is de-asserted, RX_ER has no
effect on the MAC.
TXD[1:0] transitions synchronously with respect to
REF_CLK. When TX_EN is asserted, TXD[1:0] are
accepted for transmission by the PHY. TXD[1:0] is ”00” to
indicate idle when TX_EN is de-asserted. Values other than
“00” on TXD[1:0] while TX_EN is de-asserted are ignored by
the PHY.
Carrier Sense/Receive Data Valid (CRS_DV)
CRS_DV is asserted by the PHY when the receive medium
is non-idle. It is asserted asynchronously on detection of
carrier. This is when squelch is passed in 10Mbps mode,
and when 2 non-contiguous zeroes in 10 bits are detected
in 100Mbps mode. Loss of carrier results in the de-assertion
of CRS_DV. So long as carrier detection criteria are met,
CRS_DV remains asserted continuously from the first
recovered di-bit of the frame through the final recovered
di-bit, and it is negated prior to the first REF_CLK that
IDT™ / ICS™ 10BASE-T/100BASE-TX INTEGRATED PHYCEIVER WITH RMII INTERFACE 10
ICS1894-40
REV C 092909
IDT [ INTEGRATED DEVICE TECHNOLOGY ]
