8051-mcu-debug

# 8051 MCU Debug ## Overview Use this skill to debug 8051-compatible microcontrollers and 51 MCU firmware systematically. Start by identifying the exact chip family, clock source, download method, toolchain, and failure phase, then prefer observable checks such as reset behavior, UART logs, GPIO toggles, interrupts, and SFR state before changing fuses or boot settings. ## When To Use Use this skill when: - The target is an 8051-compatible MCU, such as STC 89/90/12/15/8 series, Nuvoton N76/N79, Silicon Labs C8051, AT89, WCH 8051-like parts, or classic MCS-51 derivatives. - The user mentions 51 单片机, 8051, Keil C51, SDCC, STC-ISP, ISP/IAP, UART download, `REG52.H`, `intrins.h`, SFR, interrupt vectors, timers, or serial debugging. - Firmware cannot download, does not run after reset, has no serial output, timer/interrupt behavior is wrong, or peripherals do not respond. Do not use this skill when: - The target is Cortex-M, RISC-V, AVR, ESP32, embedded Linux, or another non-8051 architecture. - The task is only generic C syntax cleanup and does not depend on MCU behavior. - The user wants to change lock bits, fuses, clock source, or boot configuration before collecting baseline evidence. ## First Questions Ask for the minimum context needed: - Exact MCU model and board name. - Toolchain: Keil C51, SDCC, IAR, vendor IDE, or other. - Download tool: STC-ISP, Nu-Link, C2 debugger, USB programmer, UART bootloader, or ISP adapter. - Current symptom: cannot download, no boot, n...