diff --git a/src/memory/mos652x/cia.rs b/src/memory/mos652x/cia.rs
index 9b0d922..6d961a7 100644
--- a/src/memory/mos652x/cia.rs
+++ b/src/memory/mos652x/cia.rs
@@ -74,10 +74,11 @@ pub struct Cia {
   time_clock: TimeClock,
   shift_register: ShiftRegister,
   interrupts: InterruptRegister,
+  interrupt_connected: bool,
 }
 
 impl Cia {
-  pub fn new(port_a: Box<dyn Port>, port_b: Box<dyn Port>) -> Self {
+  pub fn new(port_a: Box<dyn Port>, port_b: Box<dyn Port>, interrupt_connected: bool) -> Self {
     Self {
       a: PortRegisters::new(port_a),
       b: PortRegisters::new(port_b),
@@ -86,6 +87,7 @@ impl Cia {
       time_clock: TimeClock::new(),
       shift_register: ShiftRegister::new(),
       interrupts: InterruptRegister::new(),
+      interrupt_connected,
     }
   }
 }
@@ -228,7 +230,11 @@ impl Memory for Cia {
 
     // TODO: stuff based on ca1, ca2, cb1, cb2
 
-    active_interrupt
+    if self.interrupt_connected {
+      active_interrupt
+    } else {
+      ActiveInterrupt::None
+    }
   }
 }
 
@@ -240,7 +246,7 @@ mod tests {
 
   #[test]
   fn test_read_write() {
-    let mut cia = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut cia = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // writes without DDR shouldn't be reflected in reads
     cia.write(0x00, 0b10101010);
@@ -266,7 +272,7 @@ mod tests {
 
   #[test]
   fn test_timer_a() {
-    let mut cia = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut cia = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // enable timer A interrupts
     cia.write(0x0D, interrupt_bits::MASTER | interrupt_bits::TIMER_A);
@@ -290,9 +296,34 @@ mod tests {
     }
   }
 
+  #[test]
+  fn test_interrupt_disconnected() {
+    let mut cia = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()), false);
+
+    // enable timer A interrupts
+    cia.write(0x0D, interrupt_bits::MASTER | interrupt_bits::TIMER_A);
+
+    // set the timer to count down from 0x10
+    cia.write(0x04, 0x10);
+    cia.write(0x05, 0x00);
+
+    // start the timer, and disable continuous operation
+    cia.write(0x0E, 0b0000_1001);
+
+    for _ in 0..0x0F {
+      assert_eq!(ActiveInterrupt::None, cia.poll(1, 0));
+    }
+
+    assert_eq!(ActiveInterrupt::None, cia.poll(1, 0));
+
+    for _ in 0..0x20 {
+      assert_eq!(ActiveInterrupt::None, cia.poll(1, 0));
+    }
+  }
+
   #[test]
   fn test_timer_b() {
-    let mut cia = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut cia = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // enable timer B interrupts
     cia.write(0x0D, interrupt_bits::MASTER | interrupt_bits::TIMER_B);
@@ -313,7 +344,7 @@ mod tests {
 
   #[test]
   fn test_timer_a_continuous() {
-    let mut cia = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut cia = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // enable timer A interrupts
     cia.write(0x0D, interrupt_bits::MASTER | interrupt_bits::TIMER_A);
@@ -336,7 +367,7 @@ mod tests {
 
   #[test]
   fn test_ier_timers() {
-    let mut cia = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut cia = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // enable timer 1 interrupts
     cia.write(0x0D, interrupt_bits::MASTER | interrupt_bits::TIMER_A);
@@ -363,7 +394,7 @@ mod tests {
 
   #[test]
   fn test_interrupt_flags() {
-    let mut cia = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut cia = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // enable timer 1 interrupts
     cia.write(0x0D, interrupt_bits::MASTER | interrupt_bits::TIMER_A);
diff --git a/src/memory/mos652x/pia.rs b/src/memory/mos652x/pia.rs
index 415f501..0d8ffd8 100644
--- a/src/memory/mos652x/pia.rs
+++ b/src/memory/mos652x/pia.rs
@@ -128,14 +128,16 @@ pub mod pia_control_bits {
 pub struct Pia {
   a: PiaPortRegisters,
   b: PiaPortRegisters,
+  interrupt_connected: bool,
 }
 
 impl Pia {
   /// Create a new PIA with the two given port implementations.
-  pub fn new(a: Box<dyn Port>, b: Box<dyn Port>) -> Self {
+  pub fn new(a: Box<dyn Port>, b: Box<dyn Port>, interrupt_connected: bool) -> Self {
     Self {
       a: PiaPortRegisters::new(a),
       b: PiaPortRegisters::new(b),
+      interrupt_connected,
     }
   }
 }
@@ -170,7 +172,7 @@ impl Memory for Pia {
     let a = self.a.poll(cycles_since_poll, total_cycle_count);
     let b = self.b.poll(cycles_since_poll, total_cycle_count);
 
-    if a || b {
+    if self.interrupt_connected && (a || b) {
       ActiveInterrupt::IRQ
     } else {
       ActiveInterrupt::None
@@ -186,7 +188,7 @@ mod tests {
 
   #[test]
   fn test_read() {
-    let mut pia = Pia::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut pia = Pia::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // deselect the DDR
     pia.write(0x01, pia_control_bits::DDR_SELECT);
@@ -210,7 +212,7 @@ mod tests {
 
   #[test]
   fn test_write() {
-    let mut pia = Pia::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut pia = Pia::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // deselect the DDR
     pia.write(0x01, pia_control_bits::DDR_SELECT);
diff --git a/src/memory/mos652x/via.rs b/src/memory/mos652x/via.rs
index 343ffac..f422e65 100644
--- a/src/memory/mos652x/via.rs
+++ b/src/memory/mos652x/via.rs
@@ -46,6 +46,7 @@ pub struct Via {
   sr: ShiftRegister,
   interrupts: InterruptRegister,
   pcr: u8, // peripheral control register
+  interrupt_connected: bool,
 }
 
 #[allow(dead_code)]
@@ -61,7 +62,7 @@ pub mod interrupt_bits {
 }
 
 impl Via {
-  pub fn new(a: Box<dyn Port>, b: Box<dyn Port>) -> Self {
+  pub fn new(a: Box<dyn Port>, b: Box<dyn Port>, interrupt_connected: bool) -> Self {
     Self {
       a: PortRegisters::new(a),
       b: PortRegisters::new(b),
@@ -70,6 +71,7 @@ impl Via {
       sr: ShiftRegister::new(),
       interrupts: InterruptRegister::new(),
       pcr: 0,
+      interrupt_connected,
     }
   }
 }
@@ -250,7 +252,11 @@ impl Memory for Via {
       }
     }
 
-    active_interrupt
+    if self.interrupt_connected {
+      active_interrupt
+    } else {
+      ActiveInterrupt::None
+    }
   }
 }
 
@@ -262,7 +268,7 @@ mod tests {
 
   #[test]
   fn test_read_write() {
-    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // writes without DDR shouldn't be reflected in reads
     via.write(0x00, 0b10101010);
@@ -288,7 +294,7 @@ mod tests {
 
   #[test]
   fn test_timer_1() {
-    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // enable timer 1 interrupts
     via.write(0x0e, interrupt_bits::MASTER | interrupt_bits::T1);
@@ -311,7 +317,7 @@ mod tests {
 
   #[test]
   fn test_timer_2() {
-    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // enable timer 2 interrupts
     via.write(0x0e, interrupt_bits::MASTER | interrupt_bits::T2);
@@ -334,7 +340,7 @@ mod tests {
 
   #[test]
   fn test_t1_continuous() {
-    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // enable timer 1 interrupts
     via.write(0x0e, interrupt_bits::MASTER | interrupt_bits::T1);
@@ -361,7 +367,7 @@ mod tests {
 
   #[test]
   fn test_ier_register() {
-    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // put something in the register
     via.write(
@@ -389,7 +395,7 @@ mod tests {
 
   #[test]
   fn test_ier_timers() {
-    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // enable timer 1 interrupts
     via.write(0x0e, interrupt_bits::MASTER | interrupt_bits::T1);
@@ -410,9 +416,27 @@ mod tests {
     assert_eq!(ActiveInterrupt::IRQ, via.poll(1, 0));
   }
 
+  #[test]
+  fn test_interrupt_disconnected() {
+    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()), false);
+
+    // enable timer 1 interrupts
+    via.write(0x0e, interrupt_bits::MASTER | interrupt_bits::T1);
+
+    // set timer 1 to count down from 0x10
+    via.write(0x04, 0x10);
+    via.write(0x05, 0x00);
+    // timer 1 should interrupt first
+    for _ in 0..0x0F {
+      assert_eq!(ActiveInterrupt::None, via.poll(1, 0));
+    }
+
+    assert_eq!(ActiveInterrupt::None, via.poll(1, 0));
+  }
+
   #[test]
   fn test_ifr() {
-    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let mut via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     // enable timer 1 interrupts
     via.write(0x0e, interrupt_bits::MASTER | interrupt_bits::T1);
diff --git a/src/systems/c64/mod.rs b/src/systems/c64/mod.rs
index 2eb6550..face95e 100644
--- a/src/systems/c64/mod.rs
+++ b/src/systems/c64/mod.rs
@@ -263,9 +263,10 @@ impl BuildableSystem<C64SystemRoms, C64SystemConfig> for C64System {
         config.mapping,
         platform.clone(),
       )),
+      true,
     );
 
-    let cia_2 = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let cia_2 = Cia::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     let region6 = BankedMemory::new(selector6.clone())
       .bank(
diff --git a/src/systems/pet/mod.rs b/src/systems/pet/mod.rs
index 6369b50..e66b171 100644
--- a/src/systems/pet/mod.rs
+++ b/src/systems/pet/mod.rs
@@ -180,9 +180,9 @@ impl BuildableSystem<PetSystemRoms, PetSystemConfig> for PetSystem {
 
     let port_a = PetPia1PortA::new();
     let port_b = PetPia1PortB::new(port_a.get_keyboard_row(), config.mapping, platform);
-    let pia1 = Pia::new(Box::new(port_a), Box::new(port_b));
-    let pia2 = Pia::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
-    let via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()));
+    let pia1 = Pia::new(Box::new(port_a), Box::new(port_b), true);
+    let pia2 = Pia::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
+    let via = Via::new(Box::new(NullPort::new()), Box::new(NullPort::new()), true);
 
     let kernel_rom = BlockMemory::from_file(0x1000, roms.kernal);
 
diff --git a/src/systems/vic/mod.rs b/src/systems/vic/mod.rs
index 9b3149a..592d7cb 100644
--- a/src/systems/vic/mod.rs
+++ b/src/systems/vic/mod.rs
@@ -270,8 +270,8 @@ impl BuildableSystem<Vic20SystemRoms, Vic20SystemConfig> for Vic20System {
     let v2b = VicVia2PortB::new(v1a.get_joy_pin_3());
     let v2a = VicVia2PortA::new(v2b.get_keyboard_col(), config.mapping, platform);
 
-    let via1 = Via::new(Box::new(v1a), Box::new(NullPort::new()));
-    let via2 = Via::new(Box::new(v2a), Box::new(v2b));
+    let via1 = Via::new(Box::new(v1a), Box::new(NullPort::new()), true);
+    let via2 = Via::new(Box::new(v2a), Box::new(v2b), true);
 
     let basic_rom = BlockMemory::from_file(0x2000, roms.basic);
     let kernel_rom = BlockMemory::from_file(0x2000, roms.kernal);