Adapter

The adapter can be assembled independently using the schematic (click to download), but this option is suitable only for experienced users. If you build the adapter yourself, you take responsibility for it and for debugging it.

What's on the board

Block	Purpose
ADUM (galvanic isolation)	Isolates the T-Display side from the target side — protects the ESP32 and the laptop's USB from accidental transients on the target board.
Schottky diode U8 — BAT6402VH	Reverse-polarity / clamp protection on the target rail. Critical part — do not substitute an arbitrary Schottky without verifying current capability and forward voltage.
5V PU	Programmer-driven 5V power-up rail (toggled from Settings → Enable 5V PU on the device). Used for HART, TMPM and other 5V-only targets.
Pin headers	T-Display ↔ adapter and adapter ↔ external connector for the target wiring.

warning

Do not allow reverse polarity on the target side, especially in standalone mode. The Schottky BAT6402VH covers brief transients, not sustained reverse voltage on the supply rails.

Programmer pin map

These names are the ones referenced as progPin in target JSON descriptions and what the Custom Connection image page expects:

Adapter pin	Direction	Used for
TOOL0	UART TX → MCU	Programmer-side TX, drives MCU's RX / TOOL0 line
RX	UART RX ← MCU	Reads MCU's TX line
RESET	Output	Drives the MCU's RESET pin
FLMD0	Output	NEC / Renesas FLMD0 (mode-entry) pin
LOG_0	Output (logic)	General-purpose logic output (e.g. R8C MODE, NEC FLMD1)
LOG_1	Output (logic)	Second general-purpose logic output
VDD	Power output	Switchable target supply (3.3 V / 5 V depending on target's fixed_vdd)
5V	Power output	Always-on 5V rail when 5V PU is enabled (for HART, TMPM, …)
VOUT	Power output	Alternate power output (used by some HART configurations)
GND	Ground	Common ground; some targets also pull BOOT to GND through this rail

The full list is exposed at runtime through the Lua API:

local pins = mp.target_builder.programmer_pins("tgsn")
-- pins.power     — power-output names
-- pins.reference — ground / reference names

T-Display pinout

The T-Display ↔ adapter pinout is on the second page of the schematic PDF.

Reverse polarity — what to do

If you suspect the target was wired with reverse polarity:

1. Disconnect the target immediately.
2. Cycle USB on the T-Display (power-off, plug back in).
3. Run Settings → Pin Test to verify the adapter still drives each line.
4. If 5V PU no longer enables (I2C not ready popup or sustained 5V PU enable failed), inspect BAT6402VH and the 5V rail on the adapter — they take the hit first.

Build-it-yourself notes

• Pay attention to the Schottky BAT6402VH orientation. Wrong orientation = no protection.
• Keep the ADUM channels assigned correctly — TX/RX directions are not symmetrical.
• Verify the 5V rail loads correctly before soldering the T-Display sockets in place.

If you do not feel confident about any of this, order the pre-built adapter — see TGSN kit.