VSC864A-2
VITESSE
Data Sheet
200 Mb/s 64 x 64
Crosspoint Switch
Expandability
The VSC864A-2 can be expanded to larger crosspoint switches by configuring it so that any input can be
multiplexed to any output. The figure below is an example of a 128 x 128 crosspoint switch. The top two
VSC864A-2s (1&2) correspond to the first 64 outputs and the bottom two VSC864A-2s (3&4) correspond to
the last 64 outputs. The VSC864A-2s on the left (1&3) correspond to the first 64 inputs, and the two VSC864A-
2s on the right (2&4) correspond to the last inputs. All like outputs are then joined to form a 128 bit Z output
bus. The ability of the VSC864A-2 to tri-state its outputs will prevent contention on the Z bus.
The TRI input is configured such that when it is active on the left hand chips (which are responsible for
routing the first 64 inputs) it is inactive on the two right hand chips (which are responsible for routing the last 64
inputs). The TRI input thus functions as the MSB of a 7-bit channel address word (A-bus plus TRI). Chips can
share A-bus information. The destination (D) bus can be shared among the four chips with the local strobe for
each device being used to select which output address gets reconfigured.
The layout and placement of the VSC864A-2 is such that inputs are on the top and bottom of the chip and
outputs are to the right and left. In this way a PC board design for a large crosspoint is facilitated.
In the read mode tri-stateability on the Q-bus can be controlled with the TEST STROBE input. A "low"
level on this input will tri-state its corresponding Q-bus. In this way the Q-bus from all chips can be wire-OR'ed.
Individual TEST STROBE signals to each chip, however, are required.
Figure 8: 128 X 128 Crosspoint Switch Diagram
1st 64 Inputs
2nd 64 Inputs
Z0 - Z63
I0 - I63
A0 - A5
I64 - I127
64
A0 - A5
64
64
64
VSC864
VSC864
1st 64
Outputs
Z0 - Z63
Z0 - Z63
TRI
D0 - D5
TRI
TRI
D0 - D5
D0 - D5
6
6
1
2
I64 - I127
I0 - I63
64
64
I0 - I63
A0 - A5
I64 - I127
A0 - A5
Z64 - Z127
64
Z64 - Z127
64
2nd 64
Outputs
VSC864
VSC864
TRI
TRI
D0 - D5
D0 - D5
6
6
3
4
G52132-0 Rev. 2.0
® VITESSE Semiconductor Corporation
Page 11
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