MCP23008 register map

8-bit I2C I/O expander with interrupt output — Microchip Technology

11 registers I2C I²C 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27 8-bit reg addresses 62% bit coverage not yet human-verified

I²C address conflict. On its default address(es) this part collides with MCP23017 (0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27). You cannot put them on the same bus without changing a strap pin, using an I²C multiplexer, or moving one to a second bus. See the full address map.

Get it as a C header

pip install regforge
regforge gen MCP23008 --out ./src --driver --tests

Writes mcp23008_regs.h with every address, mask and shift below, a bus-agnostic driver skeleton, and a file of compile-time assertions that make your compiler check the bit arithmetic. No API key needed — this part ships inside the package.

Not yet human-verified. Transcribed and mechanically validated — no overlapping fields, no out-of-range bits, reset values consistent with their fields — but not yet checked line-by-line against the datasheet. Verifying it is a useful half hour.

Registers

Addr	Register	Access	Width	Reset	Description
0x00	IODIR	RW	8	0xFF	Pin direction. 1 = input, 0 = output. All pins are inputs after reset.
0x01	IPOL	RW	8	0x00	Input polarity. 1 = the GPIO register reflects the inverted pin value.
0x02	GPINTEN	RW	8	0x00	Interrupt-on-change enable, per pin
0x03	DEFVAL	RW	8	0x00	Default comparison value, used when INTCON selects comparison mode
0x04	INTCON	RW	8	0x00	Interrupt control. 1 = compare against DEFVAL, 0 = compare against the previous value.
0x05	IOCON	RW	8	0x00	Device configuration. Note there is no BANK bit here -- with a single port there is nothing to re-bank.
0x06	GPPU	RW	8	0x00	100 kOhm pull-up enable, per pin, on pins configured as inputs
0x07	INTF	RO	8	0x00	Interrupt flags. 1 = this pin caused the interrupt. Read-only.
0x08	INTCAP	RO	8	0x00	Port value captured at the time of the interrupt. Cleared by reading INTCAP or GPIO.
0x09	GPIO	RW	8	0x00	Port value. Reading returns the pin state; writing modifies the output latch.
0x0A	OLAT	RW	8	0x00	Output latch. Reading returns the latch, not the pin.

Bit layouts

Drawn MSB-first, the way the datasheet draws them. [7:5] means shift 5, width 3, mask 0xE0 — this is the notation that costs people a day when they read it backwards.

IOCON @ 0x05 — 5 fields

—7

—6

SEQOP[5]

DISSLW[4]

HAEN[3]

ODR[2]

INTPOL[1]

—0

Bits	Field	Access	Mask	Reset	Description
[5]	SEQOP	RW	0x20	0x00	Sequential operation disable. 1 = the address pointer does not increment.
[4]	DISSLW	RW	0x10	0x00	Disable slew-rate control on SDA
[3]	HAEN	RW	0x08	0x00	Hardware address enable. No effect on the I2C part; present for the SPI variant.
[2]	ODR	RW	0x04	0x00	1 = INT pin is open drain, overriding INTPOL
[1]	INTPOL	RW	0x02	0x00	INT pin polarity when ODR is 0. 0 = active low, 1 = active high.

Generated C header

What regforge gen MCP23008 writes for IOCON:

/* ------------------------------------------------------------------------ */
/* IOCON @ 0x05u  rw  8-bit  reset 0x00u */
/* Device configuration. Note there is no BANK bit here -- with a single port there is nothing to re-bank. */
/* ------------------------------------------------------------------------ */

#define MCP23008_IOCON                                 0x05u
#define MCP23008_IOCON_WIDTH                           8u
#define MCP23008_IOCON_RESET                           0x00u

/*   SEQOP bits [5] rw reset 0x00u -- Sequential operation disable. 1 = the address pointer does not increment. */
#define MCP23008_IOCON_SEQOP_SHIFT                     5u
#define MCP23008_IOCON_SEQOP_WIDTH                     1u
#define MCP23008_IOCON_SEQOP_MASK                      0x20u
#define MCP23008_IOCON_SEQOP_GET(reg)                  (((uint8_t)(reg) & 0x20u) >> 5u)
#define MCP23008_IOCON_SEQOP_SET(reg, val)             (((uint8_t)(reg) & (uint8_t)~0x20u) | (((uint8_t)(val) << 5u) & 0x20u))

/*   DISSLW bits [4] rw reset 0x00u -- Disable slew-rate control on SDA */
#define MCP23008_IOCON_DISSLW_SHIFT                    4u
#define MCP23008_IOCON_DISSLW_WIDTH                    1u
#define MCP23008_IOCON_DISSLW_MASK                     0x10u
#define MCP23008_IOCON_DISSLW_GET(reg)                 (((uint8_t)(reg) & 0x10u) >> 4u)
#define MCP23008_IOCON_DISSLW_SET(reg, val)            (((uint8_t)(reg) & (uint8_t)~0x10u) | (((uint8_t)(val) << 4u) & 0x10u))

/*   HAEN bits [3] rw reset 0x00u -- Hardware address enable. No effect on the I2C part; present for the SPI variant. */
#define MCP23008_IOCON_HAEN_SHIFT                      3u
#define MCP23008_IOCON_HAEN_WIDTH                      1u
#define MCP23008_IOCON_HAEN_MASK                       0x08u
#define MCP23008_IOCON_HAEN_GET(reg)                   (((uint8_t)(reg) & 0x08u) >> 3u)
#define MCP23008_IOCON_HAEN_SET(reg, val)              (((uint8_t)(reg) & (uint8_t)~0x08u) | (((uint8_t)(val) << 3u) & 0x08u))

/*   ODR bits [2] rw reset 0x00u -- 1 = INT pin is open drain, overriding INTPOL */
#define MCP23008_IOCON_ODR_SHIFT                       2u
#define MCP23008_IOCON_ODR_WIDTH                       1u
#define MCP23008_IOCON_ODR_MASK                        0x04u
#define MCP23008_IOCON_ODR_GET(reg)                    (((uint8_t)(reg) & 0x04u) >> 2u)
#define MCP23008_IOCON_ODR_SET(reg, val)               (((uint8_t)(reg) & (uint8_t)~0x04u) | (((uint8_t)(val) << 2u) & 0x04u))

/*   INTPOL bits [1] rw reset 0x00u -- INT pin polarity when ODR is 0. 0 = active low, 1 = active high. */
#define MCP23008_IOCON_INTPOL_SHIFT                    1u
#define MCP23008_IOCON_INTPOL_WIDTH                    1u
#define MCP23008_IOCON_INTPOL_MASK                     0x02u
#define MCP23008_IOCON_INTPOL_GET(reg)                 (((uint8_t)(reg) & 0x02u) >> 1u)
#define MCP23008_IOCON_INTPOL_SET(reg, val)            (((uint8_t)(reg) & (uint8_t)~0x02u) | (((uint8_t)(val) << 1u) & 0x02u))

Compared with

MCP23008 vs MCP23017

Related parts

Source

Transcribed from Microchip MCP23008/MCP23S08 datasheet (DS21919) (hand-transcribed) (hand-transcribed). Hand-authored seed entry, not machine-extracted. Check against Microchip MCP23008/MCP23S08 datasheet (DS21919) before trusting it, then mark it verified.

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