I/O Control Commands

AI – Arduino Input

Sets the function of the Arduino DIN pin on JP1.

Syntax

AIn
AI?

Parameters

Value	Function
0	Disabled (no function)
1	Squelch open input
2	PTT input

Default

0 (Disabled)

Examples

AI0             # Disable DIN function
AI2             # Use DIN as PTT input
AI?             # Query current function

Notes

• When AI2, grounding DIN keys the transmitter
• When AI1, DIN state reports squelch to external device
• DIN accepts 3.3V or 5V logic levels

Related Commands

• AO — Arduino output pin

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AO – Arduino Output

Sets the function of the Arduino DOUT pin on JP1.

Syntax

AOn
AO?

Parameters

Value	Function
0	Always LOW
1	HIGH when squelch open
2	HIGH when DTMF detected
3	HIGH when transmitting (TX ON)
4	HIGH when CTCSS detected
5	Always HIGH
6	HIGH when VOX triggered (firmware 2.4+)

Default

0 (LOW)

Examples

AO0             # DOUT always low
AO1             # DOUT high when squelch opens
AO3             # DOUT high during TX
AO?             # Query current function

Notes

• Output voltage is 2–5V based on VIO pin
• Useful for LED indicators or controller inputs
• AO2 requires DTMF detection enabled (DR1)
• AO4 requires CTCSS mode enabled (TM2)

Applications

Setting	Use Case
AO1	Busy LED, COR indicator
AO2	DTMF command trigger
AO3	TX indicator LED
AO4	Selective call indicator

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EX – External Pins

Sets the function of E_TX and E_RX pins on the DE-9 I/O connector.

Syntax

EXn
EX?

Parameters

Value	E_TX (pin 7)	E_RX (pin 8)
0	HIGH when TX	LOW when squelch open
1	Serial TXD	Serial RXD

Default

1 (TTL Serial Port)

Examples

EX1             # Use as serial port (default)
EX0             # Use as TX/SQ indicators
EX?             # Query current function

Serial Mode (EX1)

• Pin 7 (E_TX): Serial data OUT (connect to device RX)
• Pin 8 (E_RX): Serial data IN (connect to device TX)
• Baud rate set by B2 command

Indicator Mode (EX0)

• Pin 7 (E_TX): HIGH during transmit, LOW during receive
• Pin 8 (E_RX): LOW when squelch open, HIGH when closed

Notes

• Serial mode uses 3.3V logic levels
• Indicator mode useful for external controllers
• Choose mode based on what’s connected to DE-9

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LD – Status LED

Sets the function of the ST (status) LED on the board.

Syntax

LDn
LD?

Parameters

Value	Function
0	Always OFF
1	Always ON
2	ON when squelch open
3	Battery charge status (legacy)
4	ON when VOX triggered (firmware 2.4+)

Default

2 (Squelch open)

Examples

LD0             # LED off
LD2             # LED on when signal received
LD?             # Query current function

Notes

• The RS-UV3A has three LEDs: PWR, TX, and ST
• PWR and TX are fixed function
• Only ST LED is user-configurable
• LD3 is a legacy function for older boards with battery charging