Figures 5 and 6 and the

I/O Interface Characteristics

show the timing details of the 3-wire interface. If the two

command bits initiate a SWITCHSET command, a logic

“1” in a switch control location closes the associated

switch, while a logic “0” opens it. If the command bits ini-

tiate a MODESET command, a logic “1” in a switch con-

trol location sets the associated switch into soft

“clickless” mode, while a logic “0” sets it into hard mode.

For command-bit configurations, see Table 1.

Using Multiple Devices

There are two ways to connect multiple devices to the

same 3-wire serial interface. The first involves using the

DOUT pin. DOUT presents a copy of the last bit of the

internal shift register, useful for daisy-chaining multiple

devices. Data at DOUT are simply the input data

delayed by eight clock cycles, appearing synchronous

with SCLK’s falling edge. After CS goes high, DOUT

holds the last bit in the shift register until new data are

shifted into DIN. For a simple interface using several

MAX4563 devices, daisy-chain the shift registers by

connecting DOUT of the first device to DIN of the sec-

ond, etc. Connect the CS pins of all devices together.

Data are shifted through the MAX4563 in series. When

CS is brought high, all devices are updated simultane-

ously. If any of the devices in the chain are to be left

unchanged, use a NO_OP command for that device, as

shown in Table 1.

An alternate way of connecting multiple devices is to

decode the CS line. In this case, do not use the DOUT

pin and connect the DIN pins of all devices together.

Address decode logic individually controls the CS line

of each device. When a device is to be selected, its CS

line is brought low, data are shifted in, and its CS line is

then brought high to execute the command.

For command bit configuration see Table 1.

T-Switches

Configure the MAX4562/MAX4563 as a T-switch to

improve off-isolation. As the signal frequency is in-

creased, parasitic capacitance significantly degrades

the off-isolation. Figure 7 shows a typical T-switch con-

figuration using the MAX4562/MAX4563 to improve off-

isolation. COM2 and COM3 are tied together to create

a single common node. NO2A and NO2B act as the

input and output of the T-switch, while NO3 is tied to

ground. When both SW2A and SW2B are closed, SW3

should be open to allow the signal to pass into NO2A

and out of NO2B. However, when SW2A and SW2B are

open, energy that is coupled through the open switch-

es is shunted to ground through SW3, which should

now be closed. This increases the off-isolation to typi-

cally -68dB at 10MHz (Figure 8).

Serially Controlled, Clickless

Audio/Video Switches

12

______________________________________________________________________________________

Table 3. MAX4562 2-Wire Serial-Interface Data Format

Table 4. MAX4563 3-Wire Serial-Interface

Data Format

SWITCH CONTROL

COMMAND

D1

D3

D0

MSB

LSB

D2

D5

D4

D6

D7

SW3

SW2A

SW4

SW3B

SW1A SW1B

C0

C1

1

SRT

STP = Stop Condition

Logic “0” in any data bit location places the associated switch open or in hard switching mode.

Logic “1” in any data bit location places the associated switch closed or in soft (clickless) switching mode.

See Table 1 for command-bit configuration.

1

0

0

1

C1

A1

A0

0

ACK

C0

SW2A SW1B

SW2B

SW3

SW4

ACK

STP

SW2A

ADDRESS BYTE

COMMAND BYTE

MSB

LSB

MSB

LSB