MCP23S17

IO expander / level shift

MCP23S17 16-bit SPI I/O expander (28-pin DIP) — two 8-bit ports (GPA/GPB) with interrupts.

Manufacturer datasheet

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Specifications

No specs listed.

Pinout

Pin	Name	Functions	Notes
1	GPB0	GPIO	Port B0
2	GPB1	GPIO	Port B1
3	GPB2	GPIO	Port B2
4	GPB3	GPIO	Port B3
5	GPB4	GPIO	Port B4
6	GPB5	GPIO	Port B5
7	GPB6	GPIO	Port B6
8	GPB7	GPIO	Port B7
9	VDD	POWER	Supply
10	VSS	GND	Ground
11	CS	SPI	Chip select
12	SCK	SPI	SPI clock
13	SI	SPI	MOSI
14	SO	SPI	MISO
15	A0	GPIO	Address 0
16	A1	GPIO	Address 1
17	A2	GPIO	Address 2
18	RESET	GPIO	Reset
19	INTB	GPIO	Port B interrupt
20	INTA	GPIO	Port A interrupt
21	GPA0	GPIO	Port A0
22	GPA1	GPIO	Port A1
23	GPA2	GPIO	Port A2
24	GPA3	GPIO	Port A3
25	GPA4	GPIO	Port A4
26	GPA5	GPIO	Port A5
27	GPA6	GPIO	Port A6
28	GPA7	GPIO	Port A7

Interactive pinout

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MCP23S17

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Starter code

Community starter examples — minimal, unofficial, and provided to get you wiring fast. Verify against the manufacturer datasheet before relying on them.

Arduino (C++)

Arduino library: Adafruit MCP23017 Arduino Library

arduino

// MCP23S17 16-bit SPI I/O expander — community starter example
#include <Adafruit_MCP23X17.h>

Adafruit_MCP23X17 mcp;

#if defined(ESP32)
  #define CS_PIN 5
#else
  #define CS_PIN 10
#endif

void setup() {
  Serial.begin(115200);
  if (!mcp.begin_SPI(CS_PIN)) { Serial.println("MCP23S17 not found"); while (1) delay(10); }
  mcp.pinMode(0, OUTPUT);          // port A, pin 0
  mcp.pinMode(8, INPUT_PULLUP);    // port B, pin 0
}

void loop() {
  mcp.digitalWrite(0, HIGH);
  delay(300);
  mcp.digitalWrite(0, LOW);
  delay(300);
  Serial.println(mcp.digitalRead(8));
}

MicroPython

python

# MCP23S17 SPI I/O expander (ESP32) — community starter example
# No common MicroPython driver: raw SPI register writes (IODIRA/GPIOA ...)
from machine import Pin, SPI
import time

spi = SPI(2, baudrate=1000000, sck=Pin(18), mosi=Pin(23), miso=Pin(19))
cs = Pin(5, Pin.OUT, value=1)
OPCODE = 0x40   # device 0, write

def write_reg(reg, val):
    cs.value(0); spi.write(bytes([OPCODE, reg, val])); cs.value(1)

write_reg(0x00, 0x00)   # IODIRA: all of port A = outputs
while True:
    write_reg(0x12, 0xFF); time.sleep(0.3)   # GPIOA high
    write_reg(0x12, 0x00); time.sleep(0.3)   # GPIOA low

Wiring

Pin	Arduino Uno R3	ESP32 DevKitC (WROOM-32)	Notes
VDD	+5V	3V3	1.8-5.5 V
VSS	GND	GND
SCK	D13 (SCK)	GPIO18
SI	D11 (MOSI)	GPIO23	SPI data in
SO	D12 (MISO)	GPIO19	SPI data out
CS	D10	GPIO5	Chip select
RESET	-	-	Tie to VDD (active-low)

Typical uses

16 extra GPIO over SPI (faster than I2C)
Button matrices and LED banks