Peripheral settings: pins, pulls, speed and board options

GPIO.Mode(pin, GPIO.Output) and SPI.Open(bus, hz) cover most projects. When you need more — a sensor on other pins, a pull-up turned off, a stronger LED driver, an inverted UART — every peripheral takes a configuration object with all the settings. This guide shows how to use them step by step. The full list of properties is in Peripheral configuration.

You need MicroCS 1.12 or newer on a board, or just the PC simulator (Try MicroCS on the PC): mcs --sim --sim-virtual script.cs accepts and checks every setting.

In MicroCS Studio open Templates (Alt+T): each peripheral's category (GPIO, PWM, ADC, UART, I2C, SPI, Board and system) has ready-to-run versions of the examples below (button, LED, open drain, I2C / SPI / UART on your own pins, PWM, ADC, board options), or type the snippets gpiocfg, i2ccfg, spicfg, uartcfg.

1. Ask the board what it supports

Console.WriteLine(Hal.Board);
Console.WriteLine($"GPIO {Hal.Has("GPIO.Configure")}  SPI {Hal.Has("SPI.Configure")}  I2C {Hal.Has("I2C.Configure")}");
foreach (var o in Hal.Options()) Console.WriteLine(o);     // settings only this chip has

true means the board honours the whole object. On boards that print false the basic settings (frequency, mode, baud …) still work and anything else throws NotSupportedException telling you which property — nothing is ever silently ignored.

2. A GPIO with exactly the electrical setup you want

// button to ground: pull-up on, input hysteresis on
var button = new Pin(9, new GpioConfig(GPIO.Input, GPIO.PullUp) { Schmitt = true });

// LED: start ON without a glitch, strong drive, fast edges
var led = new Pin("LED", new GpioConfig(GPIO.Output) { Initial = 1, DriveMilliamps = 12, Speed = GPIO.SpeedHigh });

// change it later
led.Configure(new GpioConfig(GPIO.OpenDrain) { Pull = GPIO.PullNone });

Properties you do not set stay at the board default. If the hardware cannot do something, the message says why:

GPIO.Configure: invalid argument - DriveMa: 2, 4, 8 or 12 mA          (RP2)
GPIO.Configure: not supported - Hold: not available on STM32 GPIOs

3. Buses on your own pins

On ESP32 and RP2 the bus pins are chosen at run time:

// I2C on GPIO 8 / 9 at 400 kHz, external pull-ups on the board
I2C.Open(0, new I2cConfig(400_000, 8, 9) { PullUps = false, TimeoutMs = 20 });
Console.WriteLine(string.Join(", ", I2C.Scan(0)));

// SPI display: SCK 6, MOSI 7, no MISO needed, chip select 10 handled by MicroCS
SPI.Open(1, new SpiConfig(20_000_000, 0, 6, 7) { Cs = 10 });
SPI.Write(1, new byte[] { 0xAF });

// UART for a GPS at 9600 baud on TX 17 / RX 16 with a bigger receive buffer
UART.Open(1, new UartConfig(9600, 17, 16) { RxBuffer = 2048 });

On STM32 the pins come from CubeMX; leave them unset there.

4. Reuse and tweak settings

Configuration objects are ordinary values:

var fast = new SpiConfig(40_000_000, 0);
var slow = new SpiConfig(1_000_000, 3);
var flash = new SpiDevice(1, 5, fast);      // CS 5, re-configures the bus for every access
var adc = new SpiDevice(1, 4, slow);
Console.WriteLine(fast);                    // SpiConfig { Frequency = 40000000 }
fast.Frequency = 26_000_000;                // the object changes; Open / new SpiDevice again to apply
fast.Dma = null;                            // back to the board default

5. Board options

Settings only one chip family has are named options:

foreach (var o in Hal.Options("SPI")) Console.WriteLine(o);
// SPI.queue_size (1..16): transactions the SPI driver can queue (default 4)
SPI.Open(1, new SpiConfig(40_000_000).Set("queue_size", 8));

Set checks the name and range against the board's list.

6. PWM and ADC

// 10-bit, active-low PWM on GPIO 25 (ESP32: any pin; RP2: channel = GPIO)
PWM.Configure(0, new PwmConfig(20_000, 25) { ResolutionBits = 10, Inverted = true });
PWM.Set(0, 20_000, 0.25);

// ESP32: full 0..3.1 V range, 4 samples averaged per reading
ADC.Configure(0, new AdcConfig(ADC.Atten12dB) { Oversample = 4 });
Console.WriteLine(ADC.ReadMillivolts(0));

Troubleshooting

• NotSupportedException: ... not supported - FilterNs — the board cannot do that setting; remove it, or check Hal.Has("GPIO.Configure") and the table in Peripheral configuration.
• ArgumentOutOfRangeException when assigning — the value is outside the property's range (e.g. Mode = 4 on SPI).
• no I2C pins for this bus — the board has no default pins for that bus; set Sda / Scl (or Sck / Mosi / Miso for SPI).
• Next: move big transfers to the background with DMA.