Daisy-chaining devices allows numerous devices to use the same data interface lines by cascading the outputs of multiple ADCs from separate AD777x devices. In daisy-chain configuration, only one device has a direct connection between the DOUTx interface and the digital host.
The ability to daisy-chain devices and the limit on the number of devices that can be handled by the chain is dependent on the selected DOUTx mode and the decimation rate employed.
When operating in daisy-chain mode, it is required that all AD777x devices in the chain are correctly synchronized. See AD777x FAQ: AD777x: How to synchronize multiple AD777x? for more information
Daisy-chain can be implemented using 1 or 2 DOUT lines.
- 1 DOUT Line:
Using the FORMATx = 10 mode, DOUT2 acts as an input pin as shown in the figure below. In this case, the DOUT- pin of the AD777x devices is cascaded to the DOUT2 pin of the next device in the chain. Data readback is analogous to clocking a shift register where data is clocked on the rising edge of DCLK.
- 2 DOUT lines:
When 2 DOUTx lines are enabled, DOUT2 and DOUT3 act as input pins as shown in the figure below. In this case, data from Channels 0 to 3 use DOUT0 and DOUT2 pins, and Channels 4 to 7 use DOUT1 and DOUT3.
This format will require 2 data line connections to the digital host but will increase data speed by 2.
Note:
Daisy chain mode is only available in DOUT interface and not in SPI interface. DOUT is not a standard SPI and the ADC generates the clock in daisy chain mode.