DG538A Datasheet, PDF (16/16 Pages) Vishay Siliconix – 4-/8-Channel Wideband Video Multiplexers

DG534A/538A
Vishay Siliconix
APPLICATIONS (CONT'D)
A typical switching threshold versus V_L is shown in Figure 15.
These devices feature an address readback (Tally) facility,
whereby the last address written to the device may be output
to the system. This allows improved status monitoring and
hand shaking without additional external components.
This function is controlled by the I/O pin, which directly
addresses the tri-state buffers connected to the EN and
address pins. EN and address pins can be assigned to accept
data (when I/O = 0; WR = 0; RS = 1), or output data (when I/O =
1; WR = 1; RS = 1), or to reflect a high impedance and latched
state (when I/O = 0; WR = 1; RS = 1).
When I/O is high, the address output can sink or source
current. Note that V_L is the logic high output condition. This
point must be respected if V_L is varied for input logic threshold
shifting.
Further control pins facilitate easy microprocessor interface.
On chip address, data latches are activated by WR, which
serves as a strobe type function eliminating the need for
peripheral latch or memory I/O port devices. Also, for ease of
interface, a direct reset function (RS) allows all latches to be
cleared and switches opened. Reset should be used during
power up, etc., to avoid spurious switch action. See Figure 16.
Channel address data can only be entered during WR low,
when the address latches are transparent and I/O is low.
Similarly, address readback is only operational when WR and
I/O are high.
The Siliconix CLC410 Video amplifier is recommended as an
output buffer to reduce insertion loss and to drive coaxial
cables. For low power video routing applications or for unity
gain input buffers CLC111/CLC114 are recommended.
8
7
6
5
V_th
(V)
4
3
2
1
0
0 2 4 6 8 10 12 14 16 18
V_L (V)
FIGURE 15. Switching Threshold Voltage vs. V_L
Data Bus
Reset
WR
Address Bus
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16
DG534A
S_A1
S_B2
D_A
A₀, A₁
EN
RS
D_B
WR
CLC410 _{75 W}
A_V = 2
CLC410
75 W
Address
Decoder
I/O
DG534A
S_A1
S_B2
D_A
A₀, A₁
EN
RS
D_B
WR
CLC410 75 W
CLC410
75 W
Video
Bus
Data
Bus
FIGURE 16. DG534A in a Video Matrix
Document Number: 70069
S-05734—Rev. G, 29-Jan-02