diff --git a/dsp/src/iir.rs b/dsp/src/iir.rs
index ee9639e..a6af191 100644
--- a/dsp/src/iir.rs
+++ b/dsp/src/iir.rs
@@ -117,7 +117,7 @@ impl IIR {
     /// # Arguments
     /// * `xy` - Current filter state.
     /// * `x0` - New input.
-    pub fn update(&self, xy: &mut Vec5, x0: f32) -> f32 {
+    pub fn update(&self, xy: &mut Vec5, x0: f32, hold: bool) -> f32 {
         let n = self.ba.len();
         debug_assert!(xy.len() == n);
         // `xy` contains       x0 x1 y0 y1 y2
@@ -128,7 +128,11 @@ impl IIR {
         // Store x0            x0 x1 x2 y1 y2
         xy[0] = x0;
         // Compute y0 by multiply-accumulate
-        let y0 = macc(self.y_offset, xy, &self.ba);
+        let y0 = if hold {
+            xy[n / 2 + 1]
+        } else {
+            macc(self.y_offset, xy, &self.ba)
+        };
         // Limit y0
         let y0 = max(self.y_min, min(self.y_max, y0));
         // Store y0            x0 x1 y0 y1 y2
diff --git a/src/bin/dual-iir.rs b/src/bin/dual-iir.rs
index 4a27d48..520d5ec 100644
--- a/src/bin/dual-iir.rs
+++ b/src/bin/dual-iir.rs
@@ -4,6 +4,8 @@
 
 use stm32h7xx_hal as hal;
 
+pub use embedded_hal::digital::v2::InputPin;
+
 use stabilizer::hardware;
 
 use miniconf::{minimq, Miniconf, MqttInterface};
@@ -12,7 +14,7 @@ use serde::Deserialize;
 use dsp::iir;
 use hardware::{
     Adc0Input, Adc1Input, AfeGain, CycleCounter, Dac0Output, Dac1Output,
-    NetworkStack, AFE0, AFE1,
+    DigitalInput1, NetworkStack, AFE0, AFE1,
 };
 
 const SCALE: f32 = i16::MAX as _;
@@ -39,6 +41,7 @@ impl Default for Settings {
 const APP: () = {
     struct Resources {
         afes: (AFE0, AFE1),
+        di1: DigitalInput1,
         adcs: (Adc0Input, Adc1Input),
         dacs: (Dac0Output, Dac1Output),
         mqtt_interface:
@@ -90,6 +93,7 @@ const APP: () = {
             adcs: stabilizer.adcs,
             dacs: stabilizer.dacs,
             clock: stabilizer.cycle_counter,
+            di1: stabilizer.digital_inputs.1,
         }
     }
 
@@ -109,7 +113,7 @@ const APP: () = {
     ///
     /// Because the ADC and DAC operate at the same rate, these two constraints actually implement
     /// the same time bounds, meeting one also means the other is also met.
-    #[task(binds=DMA1_STR4, resources=[adcs, dacs, iir_state, iir_ch], priority=2)]
+    #[task(binds=DMA1_STR4, resources=[adcs, di1, dacs, iir_state, iir_ch], priority=2)]
     fn process(c: process::Context) {
         let adc_samples = [
             c.resources.adcs.0.acquire_buffer(),
@@ -121,13 +125,17 @@ const APP: () = {
             c.resources.dacs.1.acquire_buffer(),
         ];
 
+        let hold = c.resources.di1.is_high().unwrap();
+
         for channel in 0..adc_samples.len() {
             for sample in 0..adc_samples[0].len() {
-                let x = f32::from(adc_samples[channel][sample] as i16);
-                let mut y = x;
+                let mut y = f32::from(adc_samples[channel][sample] as i16);
                 for i in 0..c.resources.iir_state[channel].len() {
-                    y = c.resources.iir_ch[channel][i]
-                        .update(&mut c.resources.iir_state[channel][i], y);
+                    y = c.resources.iir_ch[channel][i].update(
+                        &mut c.resources.iir_state[channel][i],
+                        y,
+                        hold,
+                    );
                 }
                 // Note(unsafe): The filter limits ensure that the value is in range.
                 // The truncation introduces 1/2 LSB distortion.
diff --git a/src/hardware/configuration.rs b/src/hardware/configuration.rs
index 0351db9..31fb16d 100644
--- a/src/hardware/configuration.rs
+++ b/src/hardware/configuration.rs
@@ -9,12 +9,12 @@ use stm32h7xx_hal::{
 
 use smoltcp_nal::smoltcp;
 
-use embedded_hal::digital::v2::{InputPin, OutputPin};
+pub use embedded_hal::digital::v2::{InputPin, OutputPin};
 
 use super::{
     adc, afe, cycle_counter::CycleCounter, dac, design_parameters,
-    digital_input_stamper, eeprom, pounder, timers, DdsOutput, NetworkStack,
-    AFE0, AFE1,
+    digital_input_stamper, eeprom, pounder, timers, DdsOutput, DigitalInput0,
+    DigitalInput1, NetworkStack, AFE0, AFE1,
 };
 
 pub struct NetStorage {
@@ -69,6 +69,7 @@ pub struct StabilizerDevices {
     pub timestamp_timer: timers::TimestampTimer,
     pub net: NetworkDevices,
     pub cycle_counter: CycleCounter,
+    pub digital_inputs: (DigitalInput0, DigitalInput1),
 }
 
 /// The available Pounder-specific hardware interfaces.
@@ -439,6 +440,12 @@ pub fn setup(
         )
     };
 
+    let digital_inputs = {
+        let di0 = gpiog.pg9.into_floating_input();
+        let di1 = gpioc.pc15.into_floating_input();
+        (di0, di1)
+    };
+
     let mut eeprom_i2c = {
         let sda = gpiof.pf0.into_alternate_af4().set_open_drain();
         let scl = gpiof.pf1.into_alternate_af4().set_open_drain();
@@ -872,6 +879,7 @@ pub fn setup(
         adc_dac_timer: sampling_timer,
         timestamp_timer,
         cycle_counter,
+        digital_inputs,
     };
 
     // info!("Version {} {}", build_info::PKG_VERSION, build_info::GIT_VERSION.unwrap());
diff --git a/src/hardware/mod.rs b/src/hardware/mod.rs
index cc7a34a..34f092f 100644
--- a/src/hardware/mod.rs
+++ b/src/hardware/mod.rs
@@ -34,6 +34,14 @@ pub type AFE1 = afe::ProgrammableGainAmplifier<
     hal::gpio::gpiod::PD15<hal::gpio::Output<hal::gpio::PushPull>>,
 >;
 
+// Type alias for digital input 0 (DI0).
+pub type DigitalInput0 =
+    hal::gpio::gpiog::PG9<hal::gpio::Input<hal::gpio::Floating>>;
+
+// Type alias for digital input 1 (DI1).
+pub type DigitalInput1 =
+    hal::gpio::gpioc::PC15<hal::gpio::Input<hal::gpio::Floating>>;
+
 pub type NetworkStack = smoltcp_nal::NetworkStack<
     'static,
     'static,