Serially Controlled, Clickless

Audio/Video Switches

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Table 1. Command-Bit Mapping

C1

C0

COMMAND

DESCRIPTION

0

0

NO_OP

No Operation

0

1

NO_OP

No Operation

1

0

SWITCHSET

Sets specified switches open or closed.

1

1

MODESET

Sets specified switches to soft or hard mode.

Applications Information

Switch Control

The MAX4562/MAX4563 have a common command-

and control-bit structure; the only difference is the inter-

face type (2-wire or 3-wire).

The SWITCHSET command controls the open/closed

states of the various switches. MODESET controls

soft/hard-mode switch states. The NO_OP command is

useful for daisy-chaining multiple 3-wire parts.

Table 1 shows the command bits’ configuration and their

related commands. Table 2 shows the configuration of

the data bits and their related switches. After a SWITCH-

SET command is issued, a logic “1” in any data-bit loca-

tion closes the associated switch, while a logic “0”

opens it. After a MODESET command, a logic “1” in any

data-bit location sets the associated switch into soft

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

2-Wire Serial Interface

face, requiring only two I/O lines of a standard micro-

processor port for communication. These devices use

a SendByte™ protocol. The SendByte protocol consists

of one byte of address field followed by one byte of

command field.

The first byte of any 2-wire serial-interface transaction is

always the address byte. To address a given chip, the

A0 and A1 bits in the address byte (Table 3) must dupli-

cate the values present at the A0 and A1 pins of that

chip, and the rest of the address bits must be configured

as shown in Table 3. Connect the A0 and A1 pins to V+

or GND or drive them with CMOS logic levels.

The second byte is the command byte, which sets the

command being written to the device. The possible

commands are MODESET and SWITCHSET. Figures 3

and 4 and the

ing of the 2-wire serial-interface protocol. All bytes of the

transmission, whether address or command, are sent

MSB first.

The MAX4562/MAX4563 are receive-only devices and

must be controlled by a bus master device. A bus mas-

ter signals the beginning of a transmission with a start

condition by transitioning SDA from high to low while

SCL is high. The slave devices monitor the serial bus

continuously, waiting for the start condition followed by

an address byte. When a device recognizes its address

byte, it acknowledges by pulling the SDA line low for one

clock period; it is then ready to accept the command

byte. The device also issues a similar acknowledgment

after the command byte. When the master has finished

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 MAX4563 uses a 3-wire SPI/QSPI/MICROWIRE-com-

patible serial interface. An active-low chip select (CS) pin

enables the device to receive data from the serial input

pin, DIN. Command and data information are clocked in

on the rising edge of the serial clock signal (SCLK) MSB

first. A total of eight bits is needed in each write cycle.

The command code is contained in the two MSBs of the

8-bit word. The remaining bits control the switches as

shown in Table 4. While shifting in the serial data, the

device remains in its original configuration. A rising edge

on CS latches the data into the MAX4563’s internal regis-

ter, initiating the device’s change of state. Table 4 shows

the details of the 3-wire interface structure.

Table 2. Control-Bit Mapping

CONTROL BIT

SWITCH

SWITCH TERMINAL

D1

D5

SW1A

2, 3

SW3

D4

SW1B

3, 4

9, 10

D3

SW2A

6, 7

D0 (LSB)

D2

SW2B

7, 8

SW4

11, 12

SendByte is a trademark of Philips Corp.