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diff --git a/src/peripherals/avrdx-sigrow.ts b/src/peripherals/avrdx-sigrow.ts
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+++ b/src/peripherals/avrdx-sigrow.ts
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+// AVR-Dx SIGROW - Signature Row
+// Read-only factory calibration data. Pre-loaded with values that produce
+// correct temperature readings with the D3AA firmware's conversion formula.
+
+import { CPU } from 'avr8js/cpu/cpu';
+
+// Typical AVR32DD20 calibration values.
+// The firmware formula (from arch/avr32dd20.c mcu_temp_raw2cooked):
+//   temp = (sigrow_offset << 4) - measurement
+//   temp *= sigrow_slope
+//   temp += 65536 / 8
+//   temp >>= 10
+//   result is Kelvin << 6
+//
+// IMPORTANT: On AVR, the (sigrow_offset << 4) shift is done in 16-bit
+// arithmetic (int is 16-bit on AVR), so offset MUST be ≤ 0x0FFF (12-bit)
+// or the shift overflows. The datasheet specifies TEMPSENSE1 as a 12-bit value.
+//
+// With slope=0x036F (879), offset=0x0800 (2048):
+//   offset << 4 = 32768 (fits in 16 bits)
+//   At 25°C: ADC_acc16 ≈ 10548, result = 19081 → 23°C (±2°C rounding)
+//   At 80°C: ADC_acc16 ≈ 6447, result = 22601 → 78°C
+//   Range -40°C..125°C: ADC values 3092..15394, all in valid 16-bit range
+const DEFAULT_TEMPSENSE0 = 0x036F; // slope
+const DEFAULT_TEMPSENSE1 = 0x0800; // offset (12-bit)
+
+const TEMPSENSE0 = 0;
+const TEMPSENSE1 = 2;
+
+export class AVRDxSIGROW {
+  constructor(cpu: CPU, base: number, readonly slope = DEFAULT_TEMPSENSE0, readonly offset = DEFAULT_TEMPSENSE1) {
+    // TEMPSENSE0 (16-bit at 0x1104-0x1105)
+    cpu.readHooks[base + TEMPSENSE0] = () => slope & 0xFF;
+    cpu.readHooks[base + TEMPSENSE0 + 1] = () => (slope >> 8) & 0xFF;
+
+    // TEMPSENSE1 (16-bit at 0x1106-0x1107)
+    cpu.readHooks[base + TEMPSENSE1] = () => offset & 0xFF;
+    cpu.readHooks[base + TEMPSENSE1 + 1] = () => (offset >> 8) & 0xFF;
+
+    // Write hooks to prevent accidental writes
+    cpu.writeHooks[base + TEMPSENSE0] = () => true;
+    cpu.writeHooks[base + TEMPSENSE0 + 1] = () => true;
+    cpu.writeHooks[base + TEMPSENSE1] = () => true;
+    cpu.writeHooks[base + TEMPSENSE1 + 1] = () => true;
+  }
+
+  /** Compute the raw ADC result (16-bit accumulated) for a given temperature in Celsius */
+  tempCToRawADC(tempC: number): number {
+    const tempK = tempC + 273.15;
+    const kelvin6 = Math.round(tempK * 64);
+    // Reverse the firmware formula:
+    // kelvin6 = ((offset << 4) - measurement) * slope + 8192) >> 10
+    // kelvin6 << 10 = (offset << 4 - measurement) * slope + 8192
+    // (kelvin6 << 10) - 8192 = (offset << 4 - measurement) * slope
+    // measurement = (offset << 4) - ((kelvin6 << 10) - 8192) / slope
+    const measurement = (this.offset << 4) - ((kelvin6 << 10) - 8192) / this.slope;
+    return Math.max(0, Math.min(0xFFFF, Math.round(measurement)));
+  }
+}