3.4. Wiring components¶
ESP-12 adapter with only the module itself installed will act as a simple breakout board. It’s however possible to add additional pull-up / pull-down resistors for the control pins. This saves space on your breadboard but also makes typical applications easy to wire.
3.4.1. Power¶
VCC and GND pins are used for power supply of ESP8266 and adapter’s onboard pull-ups / pull-downs.
Warning
VCC supplied to the adapter has to be stabilized +3.3V. Adapter doesn’t have any kind of voltage regulator onboard.
3.4.2. RX/TX¶
These pins are used by ESP8266 UART interface.
Warning
FTDI (or similar) interface has to be used for programming. Adapter doesn’t have any kind of level converter onboard.
3.4.3. Reset¶
| Resistor type | pull-up |
| Component name onboard | R_RST |
| Recommended value | 10KΩ |
When installed, resistor keeps ESP8266 in an active state. Short RESET pin to the GND to perform reset.
3.4.4. CH_PD¶
| Resistor type | current-limiting |
| Component name onboard | R_CHPD |
| Recommended value | 100Ω |
When installed, resistor keeps ESP8266 in an active state.
Warning
If you plan to change state of CH_PD pin in your design then you probably should consider changing R_CHPD to a higher value (to make it a weak pull-up).
3.4.5. ESP8266 boot options¶
GPIO0, GPIO2 and GPIO15 pins are used to determine ESP8266 boot mode. ESP-12 adapter default pull-ups / pull-downs configuration enables most common one: normal boot from SPI flash. This can be easily changed by shorting pins according to the table and the description below.
| GPIO15 | GPIO0 | GPIO2 | Mode |
|---|---|---|---|
| L | H | H | Normal boot from SPI flash |
| L | L | H | Flash via UART |
| H | x | x | Boot from external SD-card |
- L - low level
- H - high level
- x - don’t care
Note
Resistor values recommended below are weak pull-ups which are good in most cases. Depending on your application it may be necessary to change them to strong pull-ups or other solution.
3.4.5.1. GPIO0¶
| Resistor type | pull-up |
| Component name onboard | R_IO0 |
| Recommended value | 10KΩ |
When installed, resistor keeps ESP8266 in a normal running mode. Short GPIO0 pin to the GND (at least on reboot) to enter flash mode (via UART).
3.4.5.2. GPIO2¶
| Resistor type | pull-up |
| Component name onboard | R_IO2 |
| Recommended value | 10KΩ |
When installed, resistor pulls pin GPIO2 up. GPIO2 pin needs to be pulled up at least on reboot.
3.4.5.3. GPIO15¶
| Resistor type | pull-down |
| Component name onboard | R_IO15 |
| Recommended value | 10KΩ |
When installed, resistor pulls pin GPIO15 down which triggers booting from SPI Flash. Short GPIO15 to VCC to boot from external SD-card.