AD4884BBCZ datasheet(74/116 Pages) AD

74 / 116 page

Data Sheet

AD4884

DIGITAL FEATURES

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Rev. 0 | 74 of 116

Event Detection Timing

When event detection is enabled for a channel in its general config-

uration register (see the General Configuration Register section),

the HI_DTCT and LO_DTCT signals indicate the occurrence of an

internally generated event. These signals can be routed internally

through the following paths:

►

HI_DTCT and LO_DTCT are directly accessible via an enabled

GPIO with GPIO_x_SEL set to 0b100 or 0b101, respectively, a

threshold event can be monitored externally by a digital host via

the GPIO. Logic 1 on a configured GPIO indicates detection of

an event.

►

HI_DTCT and LO_DTCT can each be routed by setting the

HI_ROUTE and LO_ROUTE bits to 1, respectively, in the general

configuration register (Address 0x1C) to allow HI_DTCT and

LO_DTCT to propagate to the LO_STATUS and HI_STATUS bits

in the device status register (see the Device Status Register

section, Address 0x14). These status bits can be monitored by

the digital host via the configuration SPI. Logic 1 on a configured

GPIO indicates the detection of an event. Each of these two

bits are independently cleared when a 1 is written to these bits.

Power cycling or device reset also result in the bits clearing.

►

HI_DTCT and LO_DTCT can each be routed by setting the

HI_ROUTE and LO_ROUTE bits to 1, respectively, in the general

configuration register (Address 0x1C) to allow HI_DTCT and

LO_DTCT to propagate to the ALERT signal. Any enabled GPIO

set to output a status alert, that is, with GPIO_x_SEL set to

0b0110, routes the ALERT signal to the GPIO to indicate when

an event occurs. A GPIO configured in this mode is normally

high, with a logic low indicating that an event has occurred. As

shown in the Figure 120 section, this GPIO remains low only

while the threshold level is crossed, and it returns to logic high as

soon as the threshold bound is no longer crossed, and the timing

in Figure 119 is satisfied.

Event detection is synchronous to the rising edge of the CNV+ChX.

A latency of two conversion clock cycles exists from the first

CNV+ChX edge where the analog input crosses a threshold to a

detected event that is flagged in the device status register and to

any GPIO configured to route ALERT. As is evident in Figure 118,

where both the HI_DTCT flag and ALERT routed to a GPIO are

shown, the behavior, once the threshold level is no longer crossed,

is different. When a CNV+ChX rising edge occurs where the analog

input no longer crosses the set threshold, ALERT de-asserts two

conversion cycles later, on the rising edge of CNV. Any HI_DTCT

or LO_DTCT already set is not cleared at this point. These signals

are only cleared by writing 1 to the relevant bits in the device status

Figure 119. Event Detection Timing

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