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September 11, 2000
IDT77105
Transmit Interface
Signals
TxData[7:0], TxParity
—Transmit Data. TxData[7] is the MSB.
TxSOC
—Start Of Cell. Active high signal to be asserted when
TxData contains the first byte of the cell.
TxENB
—
Enable. Active low signal to be asserted when TxData
contains valid data.
TxFull/TxClav
—Full/Cell Available. For octet (byte)-level hand-
shake control,
TxFull
is an active low signal asserted by PHY at least 4
cycles before it is no longer able to accept transmit data. For cell-level
flow control, the assertion of TxClav indicates that the PHY is capable of
receiving an entire 53-byte cell.
TxClk
—Transmit Clock. Data transfer clock to synchronize data
transfers on TxData to PHY.
TxRef
—
Transmit Reference. 8kHz input for synchronization.
Operation and Timing
Cell transmission is controlled by the external system and is synchro-
nized to TxClk. All signals are sampled on the rising edge of TxClk. Data
is transferred to the PHY using one of two handshake methods: Octet
(byte)-Level Handshake, Cell-Level Handshake. Handshake method is
selected via setting of the Register 0x00 Bit 1. Octet (byte)-level hand-
shake operates as follows:
!
The PHY indicates it can accept data by deasserting
TxFull
.
(The PHY may assert
TxFull
at any time which will indicate that
no more than 4 write cycles (bytes) will be accepted.)
!
If
TxEnb
is asserted by the external system, data is clocked into
the PHY on the rising edge of TxClk. Note that
TxEnb
must be
deasserted within 4 cycles of
TxFull
assertion, and must not be
reasserted until after
TxFull
deassertion is detected.
The "cell-level" handshake is the same as the byte-level except that
TxClav is only asserted when the PHY can accept transfer of an entire
53-byte cell. TxEnb must remain asserted until at least the last byte of
the cell. If TxClav remains asserted at the end of the cell, TxEnb may
also remain asserted, which allows uninterrupted cell transfer from the
external system to the PHY.
Receive Interface
Signals
RxData[7:0], RxParity
—Receive Data. RxData[7] is the MSB.
RxSOC
—Start Of Cell. Active high signal asserted by PHY when
RxData contains first byte of a cell.
RxEnb
—
Enable. Active low signal asserted externally to indicate
that RxData and RxSOC will be sampled at the start of the next cycle.
RxEmpty/RxClav
—Empty/Cell Available. For octet (byte)-level flow
control,
RxEmpty
is an active low signal asserted by the PHY to indi-
cate that in the current cycle there is no valid data available for delivery
over RxData[7:0]. For cell-level flow control, RxClav indicates that an
entire cell is available for immediate transfer over RxData. In both cases,
this signal indicates cycles where there is valid data on RxData/RxSOC.
For Cell-Level Handshake mode, if register 0x02, Bit 6 is set, RxClav
can be deasserted by the PHY for 4 cycles before it is no longer able to
transfer data out.
RxClk
—Receive Clock. Transfer clock provided externally to
synchronize transfers on RxData.
RxRef
—
Receive Reference. 8kHz output derived from incoming
data stream.
Figure 3 Transmit Waveform for Octet (byte)-Level Handshake
TxClk
TxSOC
TxFull
TxEnb
TxData
X
H1
H2
P44
P45
P46
P47
P48
X
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