05. Module1_Datasheets&RefManuals
Let’s demystify datasheets and reference manuals—arguably the two most important documents in embedded development. I’ll use the STM32F103C8T6 microcontroller (used in the popular "Blue Pill" board) as our reference example because its datasheet and reference manual are both freely available and well-documented.
| Document | Purpose |
|---|---|
| Datasheet | Summary of features, electrical specs, pinouts, memory |
| Reference Manual | Detailed technical info, including registers, peripherals, and configuration steps |
The datasheet gives you a high-level overview. Here’s what to focus on:
Look for the "Pin Descriptions" table and multipurpose functions.
| Pin | Label | Function 1 | Function 2 |
|---|---|---|---|
| A9 | TX | GPIO | USART1_TX |
| A10 | RX | GPIO | USART1_RX |
Tip: This helps you know which pins can be used for which peripherals.
Found in the datasheet’s "Memory Mapping" section:
| Region | Start Address | Size |
|---|---|---|
| Flash | 0x08000000 | 64 KB |
| SRAM | 0x20000000 | 20 KB |
| Peripherals | 0x40000000 | (varies) |
| System Control | 0xE000E000 | (NVIC, SCB) |
- Voltage: 2.0V to 3.6V
- I/O levels: (for logic HIGH/LOW)
- Max current per pin: Important for driving loads
This is where you’ll spend most of your time for bare-metal programming.
Every peripheral has:
- A base address (e.g.,
0x4001 0800for GPIOA) - Several offsets (e.g., MODER, ODR, IDR, etc.)
| Name | Offset | Function |
|---|---|---|
| CRL | 0x00 | Config for pins 0–7 |
| CRH | 0x04 | Config for pins 8–15 |
| IDR | 0x08 | Input Data Register |
| ODR | 0x0C | Output Data Register |
| BSRR | 0x10 | Bit Set/Reset Register |
| BRR | 0x14 | Bit Reset Register |
| LCKR | 0x18 | Lock Configuration Register |
Example: GPIOx_CRL (GPIO Configuration Register Low)
| Bits | Field Name | Description |
|---|---|---|
| 3:2 | CNF0 | Input/output config |
| 1:0 | MODE0 | Input/output mode |
- Locate CRL (pins 0–7)
- Pin 5 starts at bit 20 → bits 20–23
You need to:
- Clear existing bits:
GPIOA->CRL &= ~(0xF << 20);
- Set new mode:
GPIOA->CRL |= (0x2 << 20); // Output, push-pull
The SFR map tells you which memory addresses control which peripherals.
These are standard across STM32 devices (with minor variation).
| Peripheral | Base Address |
|---|---|
| GPIOA | 0x4001 0800 |
| GPIOB | 0x4001 0C00 |
| RCC | 0x4002 1000 |
| USART1 | 0x4001 3800 |
These addresses are used in your code like this:
#define GPIOA_CRH (_(volatile unsigned int_)0x40010804)
| Tool | Use |
|---|---|
| STM32CubeMX | Visual pin/peripheral planner |
| Datasheet + Reference Manual | Core technical docs |
| CMSIS headers | Contain all register addresses as names |
stm32f10x.h |
Auto-defines base addresses and register structs |
| Item | Use |
|---|---|
| Datasheet | Learn pinouts, features, memory sizes |
| Reference Manual | Program the MCU at the register level |
| SFR Map | Match address with function/peripheral |
| Register Fields | Control and configure hardware behaviour |