wiring_samd21g18a.md

Heltec E-ink Modules

Wiring: SAMD21G18A

✅ SAMD21G18A uses 3.3V logic. It can connect directly to the display.

Display	SAMD21G18A
VCC	3.3V
GND	GND
D/C	D2
SDI	MOSI (COPI)
CS	D4
CLK	SCK
BUSY	D5

Where are MOSI and SCK (and MISO)?

Good question. The location depends on your board.

These suggested locations are untested: I do not own either board. Please let me know if they do not work.

Arduino Zero	Arduino Nano 33 IoT

(Optional) Changing MOSI and SCK pins

All pin assignments can be changed, using an extended constructor:

DISPLAY_CLASS(DC_PIN, CS_PIN, BUSY_PIN, SDI_PIN, CLK_PIN); 

Due to hardware limitations, only certain alternate wiring pairs are valid for SDI and CLK:

SDI pin	SCK pin
2	5
2	5
2	SCK*
4	3
4	5
5	3
5	A2
10	12
11	12
11	13
12	13
A1	5
A1	A2
A1	SCK*
MISO*	5
MISO*	A2
MISO*	SCK*
MOSI*	5
SCK*	A2

_{* ICSP Header}

If your selection is invalid, your board's LED_BUILTIN will blink out an "SOS".

(Optional) Suggested additional wiring, for power saving

void setup() {
    // GPIO 7, PNP transistor
    display.useCustomPowerSwitch(7, PNP);

    //Later, when required:
    display.customPowerOff();
    display.customPowerOn();
}

(Optional) Additional wiring: MicroSD card module

✅ SAMD21 uses 3.3V logic. It can connect directly to microSD module.

void setup() {
    // Set MicroSD CS pin
    display.useSD(7);
}

Micro SD Module	SAMD21G18A
VCC	3.3V
CS	D7
MOSI	MOSI
SCK	SCK
MISO	MISO
GND	GND

MOSI and SCK pins can be changed in the display constructor (see above).

CS pin (card) must be set with useSD(cs). Any free pin may be used.

Optionally, MISO may also be set, with useSD(cs, miso).
Only certain combinations are possible, depending on which SDI and SCK pins you may have set in the constructor.

SDI pin	SCK pin	Possible MISO pins
(default)	(default)	A1, A2, MISO*
2	5	3, 4
2	5	A1, A2, MISO*
2	SCK*	A1, A2, MISO*
4	3	2, 5
4	5	2, 3
5	3	2, 4
5	A2	2, A1, MISO*, MOSI*
10	12	11, 13
11	12	10, 13
11	13	10, 12
12	13	10, 11
A1	5	2, A2, MOSI*
A1	A2	2, 5, MOSI*, SCK*
A1	SCK*	2, A2, MOSI*
MISO*	5	2, A2, MOSI*
MISO*	A2	2, 5, MOSI*, SCK*
MISO*	SCK*	2, A2, MOSI*,
MOSI*	5	A1, A2, MISO*
SCK*	A2	2, A1, MISO*, MOSI*

_{* ICSP header}

If your selection is invalid, your board's LED_BUILTIN will blink out an "SOS".