Serially Controlled, Clickless

Audio/Video Switches

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11

Table 1. Command Bit Mapping

Table 2. Data-Bit Switch Control

X = Don’t care

MSB

MSB - 1

COMMAND

DESCRIPTION

0

0

RESET

Sets all switches open and in soft switching mode.

0

1

MODESET

Sets specified switches to soft or hard mode.

1

0

NO_OP

No Operation.

1

1

SWITCHSET

Sets specified switches open or closed.

D13

X

SW8

D12

X

SW5

D11

X

SW7B

D10

15, 16

SW7A

D8

19, 20

SW6A

X

X

X

SW11

SW9

15, 16

13, 14

17, 18

18, 19

21, 22

D7

21, 22

SW4B

D6

13, 14

SW4A

D5

11, 12

SW3B

D4

9, 10

SW3A

D3

7, 8

SW2B

SW8

SW7

SW6

SW5

SW4

11, 12

10, 11

8, 9

7, 8

5, 6

D2

5, 6

SW2A

D1

3, 4

SW1B

D0 (LSB)

1, 2

SW1A

SW3

SW2

SW1

4, 5

2, 3

1, 2

DATA BIT

SWITCH

SWITCH

D9

17, 18

SW6B

SW10

20, 21

SWITCH TERMINALS

SWITCH TERMINALS

MAX4572/MAX4574

MAX4571/MAX4573

communicating with the slave, it issues a stop condition

by transitioning SDA from low to high while SCL is high.

The bus is then free for another transmission.

3-Wire Serial Interface

The MAX4573/MAX4574 use a 3-wire SPI/QSPI/

MICROWIRE-compatible serial interface. An active-low

chip-select pin, CS, enables the device to receive data

from the serial input pin, DIN. Command and data infor-

mation are clocked in on the rising edge of the serial-

clock signal (SCLK) MSB first. A total of 16 bits are

needed in each write cycle. The write cycle allows two

8-bit-wide transfers if CS remains low for the entire 16

bits. The command code is contained in the two MSBs

of the 16-bit word. The remaining bits control the

switches as shown in Table 4. While shifting in the seri-

al data, the device remains in its original configuration.

A rising edge on CS latches the data into the

MAX4573/MAX4574 internal registers, initiating the

device’s change of state. Table 4 shows the details of

the 3-wire interface data structure.

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 associat-

ed switch, while a logic 0 opens it. If the command bits

initiate a MODESET command, a logic 1 in a switch

control location sets the associated switch into hard

mode, while a logic 0 sets it into soft, “clickless” 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 16 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

MAX4573/MAX4574 devices, daisy-chain the shift reg-