ZHCSHP3 February 2018 DAC8771
PRODUCTION DATA.
This feature is useful to ensure that communication between the host processor and the DAC8771 has not been lost. It can be enabled by setting the WEN (address 0x03) bit to '1', see . The watchdog timeout period can be set using the WPD[1:0] address 0x03) bits. The timer period is based off an internal oscillator with a typical value of 8 MHz
If enabled, the chip must have an SPI frame with 0x10 as the write address byte written to the device within the programmed timeout period. Otherwise, the ALARM pin asserts low and the WDT bit (address 0x0B) of the status register is set to '1'. The WDT bit is set to '0' with a software/hardware reset, or by disabling the watchdog timer (WEN = '0'), or powering down the device.
When using multiple DAC8771 devices in a daisy-chain configuration, the open-drain ALARM pins of all devices can be connected together to form a wired-AND network. The watchdog timer can be enabled in any number of the devices in the chain although enabling it in one device in the chain should be sufficient. The wired-AND ALARM pin may get pulled low because of the simultaneous presence of different trigger conditions in the devices in the daisy-chain. The host processor should read the status register of each device to know all the fault conditions present in the chain.