MCP23S17T-E from Microchip, in a SSOP-28-208mil. Pinout and pin descriptions extracted from the manufacturer datasheet by ds2sf; symbol, footprint, and 3D from KiCad-official CAD.

Pinout

Pin	Name	Type	Function
1	GPB0	bidirectional	PORTB bit 0. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
2	GPB1	bidirectional	PORTB bit 1. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
3	GPB2	bidirectional	PORTB bit 2. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
4	GPB3	bidirectional	PORTB bit 3. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
5	GPB4	bidirectional	PORTB bit 4. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
6	GPB5	bidirectional	PORTB bit 5. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
7	GPB6	bidirectional	PORTB bit 6. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
8	GPB7	bidirectional	PORTB bit 7. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
9	VDD	power_in	Positive supply voltage. Operating range 1.8 V to 5.5 V (industrial) or 4.5 V to 5.5 V (extended, -40 to +125°C). Bypass locally with 0.1 µF.
10	VSS	power_in	Ground reference (0 V).
11	CS	input	SPI chip select, active low. Frames a SPI transaction on the MCP23S17.
12	SCK	input	SPI serial clock input (up to 10 MHz).
13	SI	input	SPI serial data input (MOSI from host).
14	SO	output	SPI serial data output (MISO to host). Typically driven only during a read cycle.
15	A0	input	Hardware address bit 0. Must be externally tied to VDD or VSS; combined with A1/A2 forms the SPI device address.
16	A1	input	Hardware address bit 1. Must be externally tied to VDD or VSS.
17	A2	input	Hardware address bit 2. Must be externally tied to VDD or VSS; up to 8 devices share the bus.
18	RESET	input	Hardware reset, active low. Must be tied high (or driven high) for normal operation; asserting low returns all registers to POR defaults.
19	INTB	output	Interrupt output for PORTB. Configurable as active-high, active-low, or open-drain (via IOCON register).
20	INTA	output	Interrupt output for PORTA. Configurable as active-high, active-low, or open-drain; can be mirrored with INTB.
21	GPA0	bidirectional	PORTA bit 0. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
22	GPA1	bidirectional	PORTA bit 1. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
23	GPA2	bidirectional	PORTA bit 2. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
24	GPA3	bidirectional	PORTA bit 3. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
25	GPA4	bidirectional	PORTA bit 4. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
26	GPA5	bidirectional	PORTA bit 5. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
27	GPA6	bidirectional	PORTA bit 6. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.
28	GPA7	bidirectional	PORTA bit 7. Bidirectional I/O pin with optional interrupt-on-change and internal weak pull-up.

Key specifications

Parameter	Value
Manufacturer	Microchip
Package	SSOP-28-208mil
Category	Interface
Pins	28

Ordering variants

Same part, different packaging or reel option.

MCP23S17T-EE/SO
MCP23S17T-E/SO
MCP23S17T-EE/SS
MCP23S17T-E/SS
MCP23S17T-EE/P
MCP23S17T-E/P
MCP23S17T-EE/ML
MCP23S17T-E/ML

CAD (KiCad official)

Symbol: MCP23S17T-E
Footprint: Package_SO:SSOP-28_5.3x10.2mm_P0.65mm
3D model: SSOP-28-208mil (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`mcp23s17t-e.step`	362 KB	You want the bare part, or you mark your own boards.
`mcp23s17t-e-etched.step`	3.0 MB	You want the part with `MCP23S17T-E` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 759 faces against 447 in the bare model. It survives export, section views, and rendering in any CAD tool, and it drops straight into KiCad or Fusion with no extra setup.

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: Microchip datasheet (48 pp, sha256 0d23e5d2e71a68cd, 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