ADGS1412

Data Sheet

Rev. 0 | Page 20 of 25

The ADGS1412 can only enter daisy-chain mode when in

address mode by sending the 16-bit SPI command, 0x2500

(see Figure 40). When the ADGS1412 receives this command,

the SDO of the device sends out the same command because

the alignment bits at SDO are 0x25, which allows multiple

daisy-connected devices to enter daisy-chain mode in a single

SPI frame. A hardware reset is required to exit daisy-chain mode.

For the timing diagram of a typical daisy-chain SPI frame, see

Figure 41. When CS goes high, Device 1 writes Command 0,

Bits[7:0] to its switch data register of, Device 2 writes Command 1,

Bits[7:0] to its switches, and so on. The SPI block uses the last

eight bits it received through SDI to update the switches. After

entering daisy-chain mode, the first eight bits sent out by SDO

on each device in the chain are 0x00. When CS goes high, the

internal shift register value does not reset back to zero.

An SCLK rising edge reads in data on SDI while data is

propagated out SDO on an SCLK falling edge. The expected

number of SCLK cycles must be a multiple of eight before CS

goes high. When this is not the case, the SPI interface sends the

last eight bits received to the switch data register.

POWER-ON RESET

The digital section of the ADGS1412 goes through an initialization

that a minimum of 120 μs from the time of power-up or reset

drop out during the 120 μs initialization phase because it may

result in incorrect operation of the ADGS1412.

0

0

1

0

0

1

0

1

0

0

0

0

0

0

0

0

SDO

0

0

1

0

0

1

0

1

0

0

0

0

0

0

0

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

SDI

SCLK

CS

Figure 40. SPI Command to Enter Daisy-Chain Mode

SDO

COMMAND3[7:0]

8’h00

COMMAND2[7:0]

COMMAND3[7:0]

COMMAND1[7:0]

COMMAND2[7:0]

COMMAND0[7:0]

COMMAND1[7:0]

SDI

SDO3

8’h00

8’h00

8’h00

8’h00

COMMAND3[7:0]

8’h00

COMMAND2[7:0]

COMMAND3[7:0]

SDO2

DEVICE 2

DEVICE 1

DEVICE 4

DEVICE 3

CS

NOTES

1. SDO2 AND SDO3 ARE THE OUTPUT COMMANDS FROM DEVICE 2 AND DEVICE 3, RESPECTIVELY.

Figure 41. Example of a SPI Frame Where Four ADGS1412 Devices Connect in Daisy-Chain Mode