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docs: consolidate RTS/DTR settings in README #5

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47 changes: 10 additions & 37 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -149,34 +149,23 @@ The MCU nets have fixed pull resistors — idle levels matter when the programme
- J1 pin **5** open → R2 holds **BOOT0 low**.
- To enter the ROM bootloader you must **actively drive BOOT0 high** (strong enough to overcome R2), then **pulse NRST low** and release.

If CH340 **RTS/DTR** are wired to your pogo `BOOT_PROGRAM` / `RST_PROGRAM` lines, set their **idle** levels so they do not fight these resistors when you are not flashing.
### CH340 RTS/DTR (STM32CubeProgrammer)

| Programmer circuit | RTS | DTR |
|--------------------|-----|-----|
| Direct drive | High | Low |
| ESP-style dual transistor (inverted) | Low | High |

### Step-by-step (STM32CubeProgrammer)

Use [STM32CubeProgrammer](https://www.st.com/en/development-tools/stm32cubeprog.html) → **UART** mode.

#### A. Manual entry (pogo + transistor reset) — recommended

1. Set UART options in CubeProgrammer **before** Connect (see table below). Use **RTS = Low** and **DTR = High** so idle serial lines match “run mode” and do not pull BOOT0 high or NRST low through your programmer.
1. Set UART options (see table below) and RTS/DTR per your programmer circuit.
2. On the pogo: drive **BOOT0 high** (J1 pin 5), pulse **reset** (J1 pin 6), release reset while BOOT0 stays high.
3. Click **Connect** in CubeProgrammer.
3. Click **Connect**.
4. **Download** `firmware/build/cube_timer_display.bin` at **`0x08000000`**.
5. Release BOOT0 (or let R2 pull it low), reset once — firmware runs.

#### B. If RTS/DTR automate boot/reset on your programmer

Typical wiring: **RTS → `BOOT_PROGRAM`**, **DTR → reset transistor → `RST_PROGRAM`**.

| Phase | RTS (BOOT0) | DTR (reset circuit) | Result on MCU |
|-------|-------------|---------------------|---------------|
| Enter bootloader | **High** | **Low** (reset) | BOOT0 high, NRST low |
| Release reset | **High** | **High** | BOOT0 high, NRST high → ROM UART bootloader |
| After flash / normal run | **Low** | **High** | BOOT0 low (R2), NRST high (R1) → user flash |

Sequence: RTS **high**, DTR **low** briefly, then DTR **high** while RTS stays **high** before Connect. After programming, set RTS **low** and DTR **high** before disconnect.

If your reset transistor is inverted (DTR **high** = reset active), swap the DTR column.

#### STM32CubeProgrammer UART settings

| Setting | Value |
Expand All @@ -189,21 +178,6 @@ If your reset transistor is inverted (DTR **high** = reset active), swap the DTR
| Data bits | **8** |
| Stop bits | **1** |
| Flow control | **Off** |
| **RTS** | **Low** *(idle — lets R2 hold BOOT0 low)* |
| **DTR** | **High** *(idle — lets R1 hold NRST high)* |

Use the RTS/DTR row as the **safe idle** for manual pogo flashing. Only drive RTS **high** / DTR **low** when you intentionally enter the bootloader (manually or via your programmer sequence).

CLI equivalent for idle lines before a manual boot entry:

```text
STM32_Programmer_CLI.exe -c port=COM3 uart=115200 parity=even rts=low dtr=high
```

4. **Run after download**
- RTS **Low**, DTR **High** (or BOOT0 released / J1 pin 5 open so R2 pulls **low**)
- Reset the MCU
- Display firmware should start

### Command line (`stm32flash`)

Expand All @@ -222,9 +196,8 @@ Replace `/dev/ttyUSB0` with your CH340 device (`COM3` on Windows, etc.).
- **BOOT0 must be high during reset** to enter the ROM bootloader, not only after the chip is running.
- **R2 (10 kΩ)** pulls BOOT0 low when J1 pin 5 is open — you need a **strong high** on `BOOT_PROGRAM` to enter the bootloader, not a weak float.
- **R1 (10 kΩ)** pulls NRST high when J1 pin 6 is open — reset is **active low** (pull NRST low, then release).
- Set CubeProgrammer **RTS Low / DTR High** at idle so CH340 does not accidentally boot or reset the chip when connecting.
- If connect fails, swap-check TX/RX against the J1 table above.
- After flashing, **BOOT0 must be low** (RTS low or pin 5 open) otherwise the chip stays in bootloader mode.
- After flashing, **BOOT0 must be low** (pin 5 open so R2 pulls low) otherwise the chip stays in bootloader mode.
- If UART is flaky, tie **3.3 V** on J1 pin 1 in addition to board power.
- You can flash with Stackmat and display wiring connected — programming uses PA9/PA10 only.

Expand Down Expand Up @@ -291,6 +264,6 @@ See [LICENSE](LICENSE) (GPL-3.0).
|------|----------------|
| Flash binary | `firmware/build/cube_timer_display.bin` @ `0x08000000` |
| Rebuild | `cd firmware && ./build.sh` |
| Flash docs | BOOT0 high + reset → UART 115200 8E1; idle RTS **Low**, DTR **High** |
| Flash docs | BOOT0 high + reset → UART 115200 8E1 |
| Config | `firmware/src/config.h` |
| Pins | `firmware/src/board_pins.h` |