ADG2108

Rev. 0 | Page 20 of 28

WRITING TO THE ADG2108

INPUT SHIFT REGISTER

The input shift register is 24 bits wide. A 3-byte write is necessary when writing to this register and is done under the control of the serial

clock input, SCL. The contents of the three bytes of the input shift register are shown in Figure 33 and described in Table 6.

X

XXXX

XX

LDSW

DB0 (LSB)

DB7 (MSB)

DATA BITS

DATA AX3 AX2 AX1 AX0 AY2 AY1 AY0

DB8 (LSB)

DB15 (MSB)

DATA BITS

1

11

0

A2

A1

A0

R/W

DB16 (LSB)

DEVICE ADDRESS

DB23 (MSB)

Figure 33. Data-Words

Table 6. Input Shift Register Bit Function Descriptions

Bit

Mnemonic

Descriptions

DB23 to DB17

1110xxx

The MSBs of the ADG2108 are set to 1110. The LSBs of the address byte are set by the state of the

three address pins, Pin A0, Pin A1, and Pin A2.

DB16

R/W

Controls whether the ADG2108 slave device is read from or written to.

If R/W = 1, the ADG2108 is being read from.

If R/W = 0, the ADG2108 is being written to.

DB15

Data

Controls whether the switch is to be opened (off ) or closed (on).

If Data = 0, the switch is opened/off.

If Data = 1, the switch is closed/on.

DB14 to DB11

AX3 to AX0

Controls I/Os X0 to X9. See Table 7 for the decode truth table.

DB10 to DB8

AY2 to AY0

Controls I/Os Y0 to Y7. See Table 7 for the decode truth table.

DB7 to DB1

X

Don’t care.

DB0

LDSW

This bit is useful when a number of switches need to be updated simultaneously.

If LDSW = 1, the switch position changes after the new word is read.

If LDSW = 0, the input data is latched, but the switch position is not changed.

As shown in Table 6, Bit DB14 to Bit DB11 control the X input/output lines, while Bit DB10 to Bit DB8 control the Y input/output lines.

Table 7 shows the truth table for these bits. Note that the full coding sequence is written out for Channel Y0, and Channel Y1 to Channel Y7

follow a similar pattern. Note also that the RESET pin must be high when writing to the device.

Table 7. Address Decode Truth Table

DB15

DATA

DB14

AX3

DB13

AX2

DB12

AX1

DB11

AX0

DB10

AY2

DB9

AY1

DB8

AY0

Switch Configuration

X

0

0

0

0

0

0

0

Reserved

X

0

0

0

1

0

0

0

Reserved

1

0

0

1

0

0

0

0

X0 to Y0 (on)

0

0

0

1

0

0

0

0

X0 to Y0 (off )

1

0

0

1

1

0

0

0

X1 to Y0 (on)

0

0

0

1

1

0

0

0

X1 to Y0 (off )

1

0

1

0

0

0

0

0

X2 to Y0 (on)

0

0

1

0

0

0

0

0

X2 to Y0 (off )

1

0

1

0

1

0

0

0

X3 to Y0 (on)

0

0

1

0

1

0

0

0

X3 to Y0 (off )

X

0

1

1

0

0

0

0

Reserved

X

0

1

1

1

0

0

0

Reserved

1

1

0

0

0

0

0

0

X4 to Y0 (on)

0

1

0

0

0

0

0

0

X4 to Y0 (off )

1

1

0

0

1

0

0

0

X5 to Y0 (on)

0

1

0

0

1

0

0

0

X5 to Y0 (off )

1

1

0

1

0

0

0

0

X6 to Y0 (on)

0

1

0

1

0

0

0

0

X6 to Y0 (off )

1

1

0

1

1

0

0

0

X7 to Y0 (on)

0

1

0

1

1

0

0

0

X7 to Y0 (off )