AN504 데이터 시트보기 (PDF) - Vishay Semiconductors

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AN504

Video Crosspoint Switch Simplifies Large Matrix Designs

Vishay Semiconductors 

AN504

Vishay Siliconix

Address Bus

A0 A1

A3 – A15

CS

Decode

B1

B0

DG884

WR

WR

8085

S1

D4 D5 D6

Data Bus

SALVO

RS

I/O A0 A3

D3

D0

Data

Result

D7 D6 D5 D4 D3 D2 D1 D0 WR

X

0

0

0

B

B

B

B

Nothing; D4 = 0

X

0

0

1

B

B

B

B

4 -bit binary data written into one of four next event latches. The latch is

decided by status of B0 and B1 lines.

X

0

1

0

X

X

X

X

Salvo pulse – updates current event latches.

X

1

0

0

X

X

X

X

Reset or clear pulse resets all latches and sets all switches to open circuit.

FIGURE 7. 8085 Microprocessor Interface

Four-bit data to be written to or read from the DG884 is applied

to the A0 – A3 input lines. These inputs are connected to D0 –

D3 of the computer data bus. Three of the higher order data bus

lines, D4,5,6 (D7 is not used at all with the DG884), are used to

gate the WRITE pulse through to either the WRITE, RESET, or

SALVO inputs. The truth table gives the implementation of the

gating shown in the circuit diagram.

To read four-bit data from the DG884 (i.e., the current event

latch status), the I/O terminal is connected to the S1 output of

the 8085. This signal provides an advance Read/Write control

to the DG884. A read operation from the above four separate

memory locations will give the status of each current event

latch. Data being read from the DG884 will appear on the four

lower data lines, D0 – D3, of the computer data bus.

Differential Applications

Although the DG884 is a single-ended 8 x 4 crosspoint, it may

be used as a differential 4 x 2 crosspoint. Address A2 defines

inputs 1 - 4 or 5 - 8, while address B1 defines the outputs,

namely 1 and 2, or 3 and 4. A suitable wideband differential

amplifier (CLC410) at the output will provide common-mode

rejection of incoming signals and charge injection thanks to the

inherent path match within the crosspoint IC.

There is also a need for wideband two-input/output crosspoint

systems when dealing with S-VHS

Document Number: 70610

05-Aug-99

www.vishay.com S FaxBack 408-970-5600

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