Data Sheet

ADGM1304

Rev. G | Page 25 of 34

Daisy-Chain Mode

The connection of several ADGM1304 devices in a daisy-chain

configuration is possible. All devices share the same CS and SCLK

lines while the SDO pin of one device forms a connection to the

SDI pin of the next device, creating a shift register. In daisy-chain

mode, the SDO signal is an 8-cycle delayed version of the SDI

signal (see Figure 52).

The ADGM1304 can only enter daisy-chain mode from address-

able mode by sending the 16-bit SPI command, 0x2500. See

Figure 52 for an example of this command. When the

ADGM1304 receives this command, the SDO pin of the devices

sends out the same command because the alignment bits at the

SDO pin are 0x25. This command allows multiple daisy-

chained 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 53. When the CS pin goes high, Device 1 writes

Command 0 to Bits[7:0] to the SWITCH_DATA register, Device 2

writes Command 1 to Bits[7:0] to the switches, and so on. The

SPI block uses the last eight bits received through the SDI pin

to update the switches. After entering daisy-chain mode, the

first eight bits sent out by the SDO pin are 0x00. When CS goes

high, the internal shift register value does not reset back to 0.

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

propagated out of the SDO pin on an SCLK falling edge. The

expected number of SCLK cycles are a multiple of eight before

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

sends the last eight bits received to the SWITCH_DATA register.

RF4

SDI

CS

RF3

RF2

SDO

ADGM1304

DEVICE 1

SPI

INTERFACE

RFC

SCLK

RF4

RF3

RF2

SDO

ADGM1304

DEVICE 2

SPI

INTERFACE

RFC

Figure 51. Two SPI-Controlled ADGM1304 Switches Connected in a Daisy-Chain Configuration

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 52. 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 53. Example of a SPI Frame when Three ADGM1304 Devices are Connected in Daisy-Chain Mode