datasheet-and-refmanual-reading

Datasheet and Reference Manual Reading

Purpose

Teach agents a systematic methodology for reading MCU datasheets and reference manuals: which sections matter for firmware, how to cross-reference pin tables with register maps, and how to avoid documentation pitfalls (errata, footnotes, conditional fields). Not merged with skills/baremetal/peripherals-from-datasheet — this skill covers how to read docs; that skill covers how to write drivers from them.

When to Use

• Starting driver work on unfamiliar silicon
• Resolving ambiguous register bit behavior
• Verifying electrical and timing constraints before PCB/firmware sign-off
• Complementing skills/baremetal/peripherals-from-datasheet (implementation focus)
• Answering "where in the RM do I find X?"

Workflow

1. Document types

Document	Primary use
Datasheet	Pinout, max ratings, package, brief features
Reference Manual (RM)	Register maps, bit fields, clock trees, peripheral behavior
Programming Manual (PM)	Cortex-M core, NVIC, MPU, debug (ARM doc)
Errata sheet	Silicon bugs that affect firmware workarounds

Read the datasheet for what exists; read the RM for how to program it.

2. First-pass reading order (RM)

1. Memory and bus architecture (address map)
2. Reset and clock control (RCC / CGU)
3. GPIO / pin multiplexing
4. Target peripheral chapter (e.g. USART, SPI, DMA)
5. NVIC / EXTI interrupt mapping table
6. Electrical characteristics (only if timing-critical)
7. Errata — search peripheral name

3. Register map extraction checklist

For each register:

• Offset from peripheral base (verify against memory map table)
• Reset value (affects read-modify-write defaults)
• Read-only / write-only / write-1-to-clear bits
• Fields that depend on mode (check "Notes" under table)
• Side effects: clearing flags, auto-clear bits, reserved must-write-0

/* Good — named constants from RM bit table */
#define USART_CR1_UE   (1U << 13)
#define USART_CR1_TE   (1U << 3)

/* Bad — magic numbers without RM citation */
*(volatile uint32_t *)0x40011000 = 0x2000;