VITESSE
SEMICONDUCTOR CORPORATION
Data Sheet
High Performance Serial
Backplane Transceiver
VSC870
Figure 8: Multi Queue Transmitter Functional Timing (with early arbitration)
WCLK
Last 13 words of current data packet
TXIN[31:0]
TXTYP[1:0]
CRQ
3
DX
D2
DX DX DX DX HDR
DX DX
1
DX
D1
D0
Minimum of 9 clock cycles
Time to select data queue
and reconfigure switch
ACK/RCLK
P0
P1
P2
P3
REN
RTM/TCLK
2.4 Receiver Operation
In Packet Mode, the receiver examines incoming words and generates the data type signals accordingly. Refer to
section 2.2 “Data Encoding Format” for the coding of these signals. If the receive word is an IDLE word, the RXWA
signal is set LOW so the FIFO can use this signal to filter out these null data words. If the receiver detects an ACK for
the connection request on the transmit side, the ACK/RCLK signal is asserted for one word clock. The RXOUT data
bus and RXTYP outputs can be tristated by asserting RXEN. CRQ words, header words, IDLE words and data words
are sent to the receiving port card. A functional timing diagram for a typical receiver operation is shown in the
following figure. See Application Note 31 for more detailed information.
Figure 9: Receive Channel Functional Timing
WCLK
RXIN[31:0]
RXTYP[1:0]
RXWA
DN CRQ idle idle
HDR
2
D1 D2
D3 D4
HDR
2
D1
D0
1
D0
1
3
0
2.5 Flow Control Channel
The transceiver can support a back pressure mechanism by providing a flow control channel. This channel
supports two logic states that are sent from the receiving port card back to the transmitting port card. The flow
control channel is time shared with the signaling between the switch chip and the transceiver for acknowledgment
and response bits for Multi Queue connection requests. Therefore, it can only guarantee to pass the state information
from the RTR pin at the receiving port card through the switch and to the REN pin at the transmitting port card. The
REN pin is also shared between the flow control channel and the transceiver’s connection request retransmission
logic. To apply backpressure to the transmitting port card, the RTR signal should be set LOW. An application for this
flow control channel is to prevent the FIFO on the receiving side from overflowing. In this case, the
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Page 24
G52190-0, Rev 4.1
01/05/01
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
