This page documents the Nintendo Switch Gamecard.

A Switch game cartridge, frontside	A Switch game cartridge, backside
Close-up of frontside PCB	Close-up of backside PCB
Close-up of stripped frontside PCB	Close-up of backside PCB

For the Gamecard partitions that can be mounted, see here.

For the Gamecard image format, see here.

For the Gamecard ASIC, see here.

Pinout

Pin	Name	Direction	Description
0	CD# (Card Detect)	Output	Single pin on cartridge side (hardwired to gnd), which bridges pin 1 (gnd) and 2 (Card Detect) on the slot side as cartridge is inserted.
1	RCLK	Output	Return clock; Game cartridge sends back CLK signal delayed by a few ns
2	CLK	Input	Clock, 25MHz
3	CS#	Input	Chip Select
4	DAT0	Inout	Data bus pin 0
5	DAT1	Inout	Data bus pin 1
6	VCC 3.3v	Input
7	DAT2	Inout	Data bus pin 2
8	DAT3	Inout	Data bus pin 3
9	VCC 1.8v	Input
10	DAT4	Inout	Data bus pin 4
11	DAT5	Inout	Data bus pin 5
12	DAT6	Inout	Data bus pin 6
13	DAT7	Inout	Data bus pin 7
14	GND
15	RST#	Input	Reset

All IO use 1.8V for logic HIGH and 0V for logic LOW.

Slot Pinout

Annotated slot pinout

The just maps the cartridge pinout onto the slot on the console.

Pin	Name
1	GND
2	CD#
3	CLK
4	RCLK
5	CS#
6	DAT1
7	DAT0
8	VCC 3.3v
9	DAT3
10	DAT2
11	VCC 1.8v
12	DAT5
13	DAT4
14	DAT6
15	DAT7
16	GND
17	RST#

Protocol

Switch game cartridges use a simple (but Nintendo proprietery) SPI-like bus with 8-bit width (DAT7..0). It is very similar to the bus interface of 3DS game cartridges, except with very different commands.

The Switch host starts a transfer by first pulling CS low, followed by clocking a byte each clock cycle. The bus data will always be ready before the rising edge of the CLK signal, so that it can be captured on the rising edge. After command bytes are written to the bus, the direction of the bus implicitly changes and the game cartridge responds. The Switch host keeps clocking while the game cartridge responds. After the transfer is ended, the CS line is pulled high again.

Commands are 16 bytes long, and followed immediately by a 4-byte CRC-32 over the command bytes. After this, the Switch stops driving the data bus, and the bus will be 'floating'. Due to the pull-ups on the bus, it will slowly converge to logic HIGH state. The Switch will clock 2 cycles to allow the bus to settle a direction change. The Switch host will then clock another cycle and if the game cartridge didn't receive the CRC OK, it will respond with "01". Otherwise it will respond with "00" and pull DAT0 low on the next cycle to signal it is busy. The Switch host will then keep clocking until the cartridge is ready.

When the game cartridge is ready to send the actual data response, it will pull the DAT0 pin high for 2 cycles to let the Switch host know. After this, the game cartridge will send the actual data response bytes.

The actual response bytes are also followed immediately by a 4-byte CRC-32 over the actual data response bytes.

A typical boot up sequence of a game cartridge (in this case, the game "1,2 Switch") looks like this:

Command	Size	Description
`5B000000000000010000000000000000`	0x200	Read sector 0, contains "HEAD" blob
`5B000000000000010000000000000000`	0x200	Read sector 0, contains "HEAD" blob
`56000000000000000000000000000000`	0x4	Read card id "AE F8 01 21"
`28000000000000000000000000000000`	0x4	Read ??? "02 00 00 00"
`A5000000000000000000000000000000`	0x4	Read ??? "00 00 00 00"
`56000000000000000000000000000000`	0x4	Read card id "AE F8 01 21"
`28000000000000000000000000000000`	0x4	Read ??? "02 00 00 00"
`5B000000380000010000000000000000`	0x200	Read sector 0x38, contains "CERT" blob
`E2000000000000000000000000000000`	0x4	Read ??? "01 00 00 00"
`E0000000000000000000000000000000`	0x200	Read crypto-challenge header
`200838A25A344F818ABB6456694D4E8D`	0	Enter crypto mode1 with HOST-RANDOM "0838A25A344F818ABB6456694D4E8D"
`7EE41FDF12C01C157CC899910673A0CF`	0x40	Encrypted crypto mode1 command, reads CART-RANDOM
`263C8230EC15FAE3CE79365BD850F4BD`	0x0	Encrypted mode1 command, enters crypto mode2 with (HOST-RANDOM, CART-RANDOM)
`B6FDA6F37FFA29E18831D0B217DFBDBE`	0x4	Encrypted mode2 command, possibly read card id?
`7B97F7DF07240AA9870E1C974336FA8A`	0x4	Encrypted mode2 command

Manufacturers

Macronix (MX): Uses package: LGA, TSOP-48; Uses card id: 0xC2
Renesas: Uses package: LGA, TSOP-48; Uses card id: 0x23
SanDisk?: Uses package: ??; Uses card id: 0x45 ?