MCP23S08-E/SO

The MCP23S08-E/SO from Microchip is an 8-bit general-purpose I/O expander designed to add remote I/O capability to an MCU via an SPI interface. The device provides 8 bidirectional I/O pins that can be individually configured as inputs or outputs, with optional internal 100kOhm pull-up resistors on input pins. The SPI interface supports clock rates up to 10MHz for fast I/O read/write access, and the sequential operation mode allows reading or writing multiple registers in a single SPI transaction by keeping the CS pin low and clocking additional bytes. The MCP23S08 features a configurable interrupt output (INT pin) that can be triggered on input pin change, with independent interrupt-on-change enable and default comparison registers for each pin. The interrupt output is configurable as active-high or active-low, and as open-drain or push-pull, providing flexibility for different system architectures. The three hardware address pins (A0-A2) allow up to 8 MCP23S08 devices to share the same SPI chip select, for a total of 64 additional I/O pins on a single SPI bus. The input polarity register allows inverting the logic level of any input pin without external components, useful for interfacing with active-low signals. The MCP23S08 is the SPI variant of the MCP23008 (I2C version), offering faster communication speed for applications that require rapid I/O access. The extended -40 to +125C temperature range supports automotive and industrial applications.

The MCP23S08-E/SO operates as an SPI-slave I/O expander with 8 bidirectional I/O pins. Key subsystems include: (1) SPI Interface – a standard SPI slave interface with CS (chip select), SCK (clock), SI (slave in/MOSI), and SO (slave out/MISO) pins; the CS pin must be low for communication; each SPI transaction consists of a control byte (opcode bit + A2-A0 address + R/W bit) followed by a register address byte and one or more data bytes; in sequential mode, the register address auto-increments after each byte, allowing multi-register transfers without releasing CS; (2) I/O Port – the 8 I/O pins (GP0-GP7) are controlled by several registers: IODIR (direction: 0=output, 1=input), GPIO (read/write data), OLAT (output latch), GPPU (pull-up enable), IPOL (input polarity inversion); (3) Interrupt Logic – each input pin can be configured for interrupt-on-change via the GPINTEN register; when the pin state differs from the DEFVAL register value, the INT pin is asserted; the INTF register identifies which pin(s) caused the interrupt; reading the GPIO or INTCAP register clears the interrupt; (4) Address Pins – the A0-A2 pins set the device’s SPI address (0-7), allowing up to 8 devices to share the same CS line; the address is included in the control byte of each SPI transaction; (5) Configuration Register – the IOCON register controls operational modes: sequential operation enable, slew rate control, interrupt polarity, open-drain interrupt, and hardware address enable.

• Keypad scanning: 8 I/O pins as 4×4 matrix inputs with interrupt-on-change waking MCU from sleep
• LED matrix: 8 outputs driving LED columns at 10MHz SPI for fast refresh of multiplexed display
• Industrial I/O: expand MCU from 32 to 40 I/O pins with 1 MCP23S08, interrupt on limit switch change
• Multi-device: 4x MCP23S08 on same CS (different A0-A2) for 32 additional I/O pins, sequential read for fast scan