EXPANDING THE NUMBER OF INPUT PORTS

Expanding the number of inputs in a switch array is accom-

plished by wire-ORing the outputs together, and TRI-

STATEing the outputs of the CLC018s that do not have their

inputs selected. The output bus should be a controlled im-

pedance transmission line with proper termination. This is

shown in Figure 12. The circuit uses a 1-of-2 decoder with

complemented outputs to control the TRI pins of the

CLC018s in the array. Thus, all CLC018s are programmed

simultaneously, and all of them, except for the one with the

selected input, are placed in the TRI-STATE mode.

EXPANDING BOTH INPUTS AND OUTPUTS

To increase both the number of inputs and outputs in an

array, apply both the input port and output port expansion

techniques simultaneously. In Figure 13, this is shown for the

case of a 24 input by 32 output switch array. Note that both

input and output busses need to be controlled impedance

transmission lines. The CS pins for rows of CLC018s are

connected together and become the row select inputs,

whereas the TRI pins are connected together for the col-

umns of CLC018s and become the column select pins.

10008820

FIGURE 11.8x16 Crosspoint Example

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