MCP23S17 SPI GPIO Expander

@@ -0,0 +1,80 @@+# MCP23S17++**Microchip** · I/O Expander · SOIC-28++The MCP23S17 is a 16-bit general-purpose I/O expander controlled over SPI. Its two 8-bit ports have configurable direction, pull-ups, polarity, and interrupt-on-change, and three hardware address pins let up to eight devices share one SPI bus. It is the SPI counterpart of the I2C MCP23017.++## Pinout++| Pin | Name | Type | Function |+|---|---|---|---|+| 1 | GPB0 | bidirectional | PORTB bit 0 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. Max sink/source 25 mA per pin. |+| 2 | GPB1 | bidirectional | PORTB bit 1 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 3 | GPB2 | bidirectional | PORTB bit 2 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 4 | GPB3 | bidirectional | PORTB bit 3 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 5 | GPB4 | bidirectional | PORTB bit 4 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 6 | GPB5 | bidirectional | PORTB bit 5 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 7 | GPB6 | bidirectional | PORTB bit 6 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 8 | GPB7 | bidirectional | PORTB bit 7 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 9 | VDD | power_in | Positive supply. Operating range 1.8 V to 5.5 V (-40 to +85 C), 2.7 V to 5.5 V (-40 to +85 C), or 4.5 V to 5.5 V (-40 to +125 C). Decouple to VSS with a local bypass capacitor. |+| 10 | VSS | power_in | Ground reference. Return for all device currents; connect to system ground plane. |+| 11 | CS | input | SPI chip select input (active-low). Frames each SPI transaction; must be driven low to enable serial communication with this device. |+| 12 | SCK | input | SPI serial clock input. Maximum 10 MHz. Clocks data into SI on the master-configured edge and out on SO. |+| 13 | SI | input | SPI serial data input (MOSI). Receives command, address and write-data bytes from the SPI master. |+| 14 | SO | output | SPI serial data output (MISO). Drives read-data back to the SPI master; high-impedance while CS is high. |+| 15 | A0 | input | Hardware address bit 0. Sets the least-significant bit of the 3-bit chip address matched during SPI transactions. Must be externally biased (tied to VDD or VSS); do not leave floating. |+| 16 | A1 | input | Hardware address bit 1. Must be externally biased (tied to VDD or VSS). |+| 17 | A2 | input | Hardware address bit 2. Must be externally biased (tied to VDD or VSS). Combined with A0/A1 allows up to eight MCP23S17 devices to share one SPI bus. |+| 18 | RESET | input | Active-low hardware reset input. Forces all registers to their POR defaults while asserted. Must be externally biased (tie to VDD through a pull-up if unused); do not leave floating. |+| 19 | INTB | output | Interrupt output for PORTB. Polarity and drive configurable as active-high, active-low, or open-drain via IOCON.INTPOL/ODR. Can be OR'd with INTA when IOCON.MIRROR = 1. |+| 20 | INTA | output | Interrupt output for PORTA. Polarity and drive configurable as active-high, active-low, or open-drain via IOCON.INTPOL/ODR. Can be OR'd with INTB when IOCON.MIRROR = 1. |+| 21 | GPA0 | bidirectional | PORTA bit 0 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 22 | GPA1 | bidirectional | PORTA bit 1 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 23 | GPA2 | bidirectional | PORTA bit 2 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 24 | GPA3 | bidirectional | PORTA bit 3 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 25 | GPA4 | bidirectional | PORTA bit 4 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 26 | GPA5 | bidirectional | PORTA bit 5 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 27 | GPA6 | bidirectional | PORTA bit 6 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |+| 28 | GPA7 | bidirectional | PORTA bit 7 bidirectional I/O. Can be enabled for interrupt-on-change and/or internal weak pull-up. Defaults to input at power-up. |++## Key specifications++| Parameter | Value |+|---|---|+| Type | 16-bit I/O expander |+| Interface | SPI (up to 10 MHz) |+| I/O | 16, two 8-bit ports (GPA/GPB) |+| Per-pin features | Direction, pull-up, polarity, interrupt-on-change |+| Addressing | 3 hardware address pins (up to 8 on a bus) |+| Supply voltage | 1.8 V to 5.5 V |+| Operating temperature | -40 C to 85 C |++## Ordering variants++- `MCP23S17SP`+- `MCP23S17E/SP`+- `MCP23S17SO`+- `MCP23S17E/SO`+- `MCP23S17T-E/SO`+- `MCP23S17SS`+- `MCP23S17E/SS`+- `MCP23S17T-E/SS`+- `MCP23S17ML`+- `MCP23S17E/ML`+- `MCP23S17T-E/ML`++## CAD (KiCad official)++- Symbol: `mcp23s17.kicad_sym`+- Footprint: `mcp23s17.kicad_mod`+- 3D model: SOIC-28 wide body from KiCad `Package_SO/SOIC-28W_7.5x17.9mm_P1.27mm`.++## Provenance++Data extracted from the manufacturer datasheet, not a distributor listing:++- **Datasheet:** [Microchip datasheet](https://ww1.microchip.com/downloads/en/DeviceDoc/20001952C.pdf) (42 pp, sha256 `14159c6f5655e943`, retrieved 2026-08-17, tier: manufacturer)+- **Extractor:** `ds2sf` (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.+- **CAD:** KiCad official libraries (CC-BY-SA 4.0).++[Datasheet PDF](docs/mcp23s17-datasheet.pdf)