The pinouts for JTAG and UART vary depending on the specific device or implementation, but there are standard configurations for these interfaces. Here’s a detailed overview:
JTAG Pinout
JTAG (Joint Test Action Group) is used for debugging, testing, and programming devices. The pinout is generally based on the IEEE 1149.1 standard but can vary slightly depending on the hardware.
| Pin Name | Description | Common Pin Number |
|---|---|---|
| TDI | Test Data In (serial input) | Pin 1 |
| TDO | Test Data Out (serial output) | Pin 3 |
| TCK | Test Clock | Pin 9 |
| TMS | Test Mode Select | Pin 7 |
| TRST | Test Reset (optional) | Pin 5 |
| GND | Ground | Pin 4 or Pin 10 |
| VCC | Voltage supply (reference voltage) | Pin 2 |
| NC | Not Connected | Various (unused pins) |
Notes:
- JTAG is often implemented using a 10-pin, 14-pin, 20-pin, or other connectors (depending on the device or board).
- Some implementations include additional pins for reset or vendor-specific features.
- Pin numbering varies between devices, so consult the device datasheet for exact specifications.
UART Pinout
UART (Universal Asynchronous Receiver-Transmitter) is a serial communication interface widely used for debugging and communication in embedded systems.
| Pin Name | Description | Common Pin Number |
|---|---|---|
| TXD | Transmit Data | Pin 2 |
| RXD | Receive Data | Pin 3 |
| GND | Ground | Pin 5 |
| VCC | Voltage supply (optional) | Pin 1 or 4 |
Notes:
- Common configurations include 4-pin, 6-pin, or 10-pin headers.
- Some UART interfaces may include additional pins like:
- RTS (Request to Send) and CTS (Clear to Send) for hardware flow control.
- Debugging or reset signals.
- Voltage levels are typically 3.3V or 5V; ensure compatibility between devices to avoid damage.
Identifying JTAG and UART Pinouts on a PCB
1. Identifying JTAG Pins
- Look for test pads or connectors labeled as
JTAG,TDI,TDO,TCK, orTMS. - Use a multimeter or continuity tester to trace connections to known components like microcontrollers or processors.
- JTAG Tools:
- Use a JTAG debugger or tools like JTAGulator to automatically identify pin functions.
2. Identifying UART Pins
- Look for labels like
TX,RX,GND, orVCCnear the header or test pads. - Use a multimeter to identify GND and check for TX/RX activity when the device is powered on.
- Tools like Bus Pirate or FTDI adapters can help identify and interface with UART.
Practical Testing
- UART Pin Testing:
- Connect a USB-to-UART adapter (e.g., FTDI, CP2102) to the suspected pins.
- Test different baud rates (common: 9600, 115200) using serial terminal software (e.g., PuTTY, minicom).
- JTAG Pin Testing:
- Use a JTAG debugger (e.g., OpenOCD or SEGGER J-Link).
- Match the pinout configuration with the debugger tool.
- Run boundary-scan tests to verify connectivity.
Safety Tips
- Double-check voltage levels (3.3V vs. 5V) to prevent damage.
- Ensure proper grounding between devices.
- Avoid short-circuiting nearby pins during probing.