How to run microcontroller program in Keil?

To run a microcontroller program in Keil µVision, you usually do one of two things:

1. Run on real hardware (flash + debug via ST-LINK/J-LINK/ULINK)

2. Run in the simulator (only for some MCUs, with limitations)

Here’s the practical workflow.

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A) Run on real hardware (recommended)

1) Create / open the project

• Open µVision → Project → Open Project… (.uvprojx)

• Or Project → New µVision Project… and select your MCU.

2) Add startup + CMSIS + device packs (if needed)

• Pack Installer (left side) → install the pack for your MCU (e.g., STM32F4xx).

• Make sure you have:

  • Startup file (startup_*.s)

  • System file (system_*.c)

  • CMSIS headers
    (Keil packs usually provide these.)

3) Build the program

• Click Build (hammer icon) or press F7

• Fix any errors until you get 0 Errors.

4) Configure the debug adapter

Go to Project → Options for Target…

Debug tab

• Select your debugger:

  • ST-Link Debugger (common for STM32)

  • J-LINK / ULINK if you have them

• Click Settings…

  • Choose interface: SWD (recommended) or JTAG

  • Set SWD clock (start lower like 1 MHz if connection is flaky)

Utilities tab

• Check Use Target Driver for Flash Programming

• Select the correct flash algorithm for your chip (Keil usually auto-adds it from the pack)

5) Start debugging (“run”)

• Click Start/Stop Debug Session (or Debug → Start/Stop Debug Session)

• Keil will:

  • connect to the target

  • download (flash) the program

  • halt at main() (depending on settings)

6) Run / step

While in debug mode:

• Run: F5

• Step: F11 (step into), F10 (step over)

• Reset: Ctrl+F5

• Set breakpoints by clicking left margin.

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B) Run in Keil Simulator (if supported)

Some MCUs/cores are supported by the built-in simulator, but most STM32 peripheral behavior is limited.

1. Options for Target → Debug

2. Select Use Simulator

3. Start debug session

4. Use Run/Step as above

Good for:

• basic C logic

• CPU register inspection
  Not great for:

• real UART/I2C/SPI, clocks, DMA, etc.

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Common gotchas (and fixes)

“Cannot connect to target”

• Make sure SWDIO/SWCLK/GND are connected (and NRST helps a lot)

• Lower SWD clock in Debug settings

• Use “Connect under reset” if available

• Ensure board is powered and grounds are common

Program downloads but doesn’t “run”

• Check clock setup (bad PLL config can lock up)

• Verify you’re not stuck in HardFault (use call stack)

• Ensure your main() is reached (breakpoint)

Flash programming fails

• Wrong flash algorithm selected (Utilities tab)

• Read-out protection enabled on some chips (need mass erase)