IO Mapping

The nXPico exposes a single IO module (ModuleId 1704) under the device node. All channels appear automatically in the I/O mapping view as soon as the device is added to the project — see Getting Started.

Every channel has a DefaultMapping name: IN0, OUT0, AN0… are used directly in ST, without declaring or mapping anything.

Digital Inputs

Channel	Parameter ID	Type	GPIO	Default mapping
Input 0	1000	BIT	GP2	IN0
Input 1	1001	BIT	GP3	IN1
Input 2	1002	BIT	GP6	IN2
Input 3	1003	BIT	GP7	IN3
Input 4	1004	BIT	GP20	IN4
Input 5	1005	BIT	GP21	IN5
Input 6	1006	BIT	GP22	IN6

Inputs are GPIO reads, sampled once per bus cycle.

Digital Outputs

Channel	Parameter ID	Type	GPIO	Default mapping
Output 0	2000	BIT	GP10	OUT0
Output 1	2001	BIT	GP11	OUT1
Output 2	2002	BIT	GP8	OUT2
Output 3	2003	BIT	GP9	OUT3
Output 4	2004	BIT	GP14	OUT4
Output 5	2005	BIT	GP15	OUT5

PWM outputs

Every digital output can be driven as PWM at runtime. The digital behaviour stays the default: nothing changes until the application asks for it.

Channel	Parameter ID	Type	Drives
PWM_ENABLE	9100	WORD (output)	bit n = output n in PWM, bit 6 = onboard LED
PWM0	9000	WORD (output)	GP10, in place of OUT0
PWM1	9001	WORD (output)	GP11, in place of OUT1
PWM2	9002	WORD (output)	GP8, in place of OUT2
PWM3	9003	WORD (output)	GP9, in place of OUT3
PWM4	9004	WORD (output)	GP14, in place of OUT4
PWM5	9005	WORD (output)	GP15, in place of OUT5
PWM_LED	9006	WORD (output)	GP25, in place of LED

These are the same six pins, not six extra outputs. PWM<n> and OUT<n> are two views of one physical output, and PWM_ENABLE decides which one commands it.

Enabling it

PWM_ENABLE := 2#0000_0100;   (* bit 2 -> OUT2 becomes a PWM output *)
PWM2       := 32768;         (* 50% duty *)

Clear the bit and the pin goes back to being a GPIO driven by OUT2.

The value is 0…65535 with no scaling: 0 is always low, 65535 is always high, whatever frequency is set. The carrier is about 2.3 kHz, from a 16-bit wrap on a 150 MHz system clock.

Changing the carrier frequency

The frequency is a device parameter, not an I/O channel: it is a plant decision — you make it knowing what is wired to the terminal — not a process value that changes every cycle. Set it in the device’s Internal Parameters tab; it is applied when the application starts.

Parameter	ID	Covers	Default
PWM frequency OUT0/OUT1	9200	GP10, GP11	2289 Hz
PWM frequency OUT2/OUT3	9201	GP8, GP9 and the LED	2289 Hz
PWM frequency OUT4/OUT5	9202	GP14, GP15	2289 Hz

One parameter per pair, not per output, because wrap and the divider are slice registers and the pins are paired onto slices. A per-output setting would be a promise the hardware cannot keep.

Range 9 Hz…100 kHz. The duty stays 0…65535 whatever the frequency: the runtime rescales it onto the slice’s real step count. What changes is the resolution underneath:

Frequency	Steps per period	Resolution
50 Hz (servo)	65217	16 bit
1 kHz	50000	15.6 bit
2289 Hz (default)	65530	16 bit
20 kHz (silent motor drive)	7500	12.9 bit
100 kHz	1500	10.6 bit

The default is the frequency that gives full 16-bit resolution. Leave it alone and nothing changes.

Two limits worth knowing

The LED shares its hardware channel with OUT3

GP25 and GP9 land on the same PWM slice and the same channel — one compare register for both. They cannot have different duty cycles. The runtime resolves it in favour of the output: while OUT3 is in PWM, bit 6 is ignored and the LED stays digital. The correction is internal to the driver: your PWM_ENABLE variable keeps the value you wrote, so the monitor still shows the bit set. The LED itself is what tells you.

The other limit is the frequency, which is the same for both outputs of a pair. Pins are paired onto slices — GP8/GP9, GP10/GP11, GP14/GP15 — and a slice has one wrap and one divider: that is why there is one parameter per pair (9200, 9201, 9202). Independent levels, frequency shared by the pair.

Measuring it

A multimeter in DC volts reads the average, so it reads duty × 3.3 V: about 1.65 V at 50%. On a digital pin an intermediate reading is itself the proof that the output is switching. If the meter has a Hz function, it should read ~2289 Hz.

nXPico only

nXPico W has the same six PWM outputs but no PWM_LED: its LED hangs off the CYW43 and is not a pin. nXPico M has the same PWM0–PWM5 outputs, PWM_ENABLE and the 9200–9202 frequencies, but no PWM_LED: there the LED is a WS2812, dimmed by writing a smaller colour value.

Analog Inputs

12-bit ADC, raw value 0…4095 — no scaling is applied by the runtime.

Channel	Parameter ID	Type	GPIO	ADC	Default mapping
Analog 0	3000	WORD	GP26	ADC0	AN0
Analog 1	3001	WORD	GP27	ADC1	AN1
Analog 2	3002	WORD	GP28	ADC2	AN2

Input range is 0…3.3 V, so one count is roughly 0.8 mV.

Onboard LED

Channel	Parameter ID	Type	GPIO	Default mapping
LED	4000	BIT (output)	GP25	LED

System

Channel	Parameter ID	Type	Access	Default mapping
Temperature	5000	REAL (input)	read	TEMPERATURE
Vendor	393218	STRING	read-only	'nexo S.r.l.'
Model Name	393219	STRING	read-only	'IO'

TEMPERATURE is the RP2350A’s internal die temperature in °C, computed from ADC4. It measures the chip, not the environment: expect it to read above ambient.

Pins not used by the I/O map

GPIO	Used by
GP0, GP1	Boot/diagnostic log (UART0 TX on GP0, 115200 8N1) — stops when your application opens COM2, until the next reboot
GP4, GP5	COM3 — free until your application opens the port
GP12, GP13	COM2 — free until your application opens the port
GP16, GP17, GP19	Free (SPI0)
GP18	DE (direction) pin of COM2 — free until your application opens the port

Note

IN0–IN6, OUT0–OUT5, AN0–AN2 and LED are the same channel set exposed by nXPico W and by nXPico M, on the same GPIOs, with two exceptions: on nXPico W the LED sits on the WiFi chip, on nXPico M it is a WS2812 RGB LED on GP23 (a DWORD channel) and there is no TEMPERATURE channel. Otherwise only the connectivity differs.

See ST Examples for sample code.