diff --git a/succbone/succd/main.go b/succbone/succd/main.go
index cfd93a9..52a10db 100644
--- a/succbone/succd/main.go
+++ b/succbone/succd/main.go
@@ -48,12 +48,6 @@ func main() {
 	if flagFake {
 		klog.Infof("Starting with fake peripherals")
 		d.adcPirani = &fakeADC{}
-		d.gpioRoughingPump = &fakeGPIO{desc: "rp"}
-		d.gpioDiffusionPump = &fakeGPIO{desc: "~dp"}
-		d.gpioBtnPumpDown = &fakeGPIO{desc: "~pd"}
-		d.gpioBtnVent = &fakeGPIO{desc: "~vent"}
-		d.gpioBelowRough = &fakeGPIO{desc: "~rough"}
-		d.gpioBelowHigh = &fakeGPIO{desc: "~high"}
 	} else {
 		adc, err := newBBADC(0)
 		if err != nil {
@@ -65,23 +59,6 @@ func main() {
 		if err != nil {
 			klog.Exitf("Failed to connect to modbus %v", err)
 		}
-
-		for _, c := range []struct {
-			out *gpio
-			num int
-		}{
-			{&d.gpioRoughingPump, 115},
-			{&d.gpioDiffusionPump, 49},
-			{&d.gpioBtnPumpDown, 48},
-			{&d.gpioBtnVent, 60},
-			{&d.gpioBelowRough, 30},
-			{&d.gpioBelowHigh, 7},
-		} {
-			*c.out, err = newBBGPIO(c.num, true)
-			if err != nil {
-				klog.Exitf("Failed to setup GPIO: %v", err)
-			}
-		}
 	}
 
 	web := webServer{
diff --git a/succbone/succd/modbus.go b/succbone/succd/modbus.go
index 15c3697..61f38de 100644
--- a/succbone/succd/modbus.go
+++ b/succbone/succd/modbus.go
@@ -63,7 +63,7 @@ func (d *daemon) modbusUpdate() error {
 	d.daemonState.tempSEM = modbusValuesToFloat(registers[0])
 	d.daemonState.humiditySEM = modbusValuesToFloat(registers[1])
 
-	// Switch to slave 2
+	// Switch to slave 2 (KEC2)
 	d.modbusClient.SetUnitId(2)
 
 	// PT100 mapping
@@ -76,18 +76,74 @@ func (d *daemon) modbusUpdate() error {
 	}
 
 	if len(registers) != 3 {
-		msg := fmt.Sprintf("Expected three registers from modbus slave 2, but got %d", len(registers))
-		return errors.New(msg)
+		return fmt.Errorf("expected three registers from modbus slave 2, but got %d", len(registers))
 	}
 
 	d.daemonState.tempDPBottom = modbusValuesToFloat(registers[0])
 	d.daemonState.tempDPInlet = modbusValuesToFloat(registers[1])
 	d.daemonState.tempDPTop = modbusValuesToFloat(registers[2])
 
+	// Switch to slave 3 (KEC1)
+	d.modbusClient.SetUnitId(3)
+
+	// Do a read first to avoid side-effects from the subsequent write to the relay states
+	var digitalInputs [8]bool
+	var digitalInputRegisters []uint16
+
+	digitalInputRegisters, err = d.modbusClient.ReadRegisters(0x81, 8, modbus.HOLDING_REGISTER)
+	if err != nil {
+		return err
+	}
+	// Convert MODBUS words into bools
+	for idx, value := range digitalInputRegisters {
+		if value != 0 {
+			digitalInputs[idx] = true
+		} else {
+			digitalInputs[idx] = false
+		}
+	}
+	// TODO: Input mapping goes here
+
+	// KFA1-KFA8
+	var relayState [8]bool
+
+	// -KFA1 Roughing Pump
+	relayState[0] = d.daemonState.rpOn
+	// -KFA2 Diffusion Pump
+	relayState[1] = d.daemonState.dpOn
+	// -KFA4 Button Vent
+	relayState[3] = d.daemonState.vent.output
+	// -KFA5 Button Pump-Down
+	relayState[4] = d.daemonState.pumpdown.output
+	// -KFA6 Fake-Pirani Rough
+	relayState[5] = d.aboveRough.output
+	// -KFA7 Fake-Pirani High
+	relayState[6] = d.aboveHigh.output
+
+	// The KEC1 module uses a non-standard MODBUS interface
+	// instead of coils
+	// 0x0100 is the open command
+	// 0x0200 is the close command
+	// We write 8 words (16-bit) to address 0x01 to update the relays
+	var registerValues [8]uint16
+	// Convert the boolean values to the commands
+	for idx, state := range relayState {
+		if state {
+			registerValues[idx] = 0x0100
+		} else {
+			registerValues[idx] = 0x0200
+		}
+	}
+
+	err = d.modbusClient.WriteRegisters(0x01, registerValues[:])
+	if err != nil {
+		return err
+	}
+
 	return nil
 }
 
-// Call modbusUpdate every second
+// Call modbusUpdate every 100 milliseconds
 func (d *daemon) modbusProcess(ctx context.Context) {
 	for {
 		select {
@@ -95,7 +151,7 @@ func (d *daemon) modbusProcess(ctx context.Context) {
 			return
 		default:
 			d.modbusUpdate()
-			time.Sleep(time.Second * 1)
+			time.Sleep(time.Millisecond * 100)
 		}
 	}
 }
diff --git a/succbone/succd/process.go b/succbone/succd/process.go
index 7ade055..7504b19 100644
--- a/succbone/succd/process.go
+++ b/succbone/succd/process.go
@@ -19,13 +19,6 @@ type daemon struct {
 	// Pirani gauge.
 	adcPirani adc
 
-	gpioDiffusionPump gpio
-	gpioRoughingPump  gpio
-	gpioBtnPumpDown   gpio
-	gpioBtnVent       gpio
-	gpioBelowRough    gpio
-	gpioBelowHigh     gpio
-
 	load atomic.Int64
 
 	// mu guards the state below.
@@ -171,33 +164,5 @@ func (d *daemon) processOnce(_ context.Context) error {
 		d.dpOn = false
 	}
 
-	// Update relay outputs.
-	for _, rel := range []struct {
-		name string
-		gpio gpio
-		// activeHigh means the relay is active high, ie. a true source will
-		// mean that NO/COM get connected, and a false source means that NC/COM
-		// get connected.
-		activeHigh bool
-		source     bool
-	}{
-		{"rp", d.gpioRoughingPump, false, d.rpOn},
-		{"dp", d.gpioDiffusionPump, true, d.dpOn},
-		{"pumpdown", d.gpioBtnPumpDown, true, d.pumpdown.output},
-		{"vent", d.gpioBtnVent, true, d.vent.output},
-		{"rough", d.gpioBelowRough, false, d.aboveRough.output},
-		{"high", d.gpioBelowHigh, false, d.aboveHigh.output},
-	} {
-		val := rel.source
-		if rel.activeHigh {
-			// Invert because the relays go through logical inversion (ie. a
-			// GPIO false is a relay trigger).
-			val = !val
-		}
-		if err := rel.gpio.set(val); err != nil {
-			return fmt.Errorf("when outputting %s: %w", rel.name, err)
-		}
-	}
-
 	return nil
 }