Wlan Application Interface; Bluetooth Application Interface; Adc Interfaces - Quectel EC21 Series Hardware Design

1. FC20 series/FC21 modules can only be used as a slave device.
2. When Bluetooth function is enabled on EC21 series module, PCM_SYNC and PCM_CLK pins are
only used to output signals. Bluetooth function is under development.
3. For more information about interfaces for WLAN and Bluetooth applications, see document [6].

3.14.1. WLAN Application Interface

EC21 series provides a low power SDIO 3.0 interface and a control interface for WLAN design. SDIO
interface supports the SDR mode, and the maximum frequency is up to 50 MHz.
As SDIO signals are high-speed, in order to ensure the SDIO interface design corresponds with the
SDIO 3.0 specification, please comply with the following principles:
It is important to route the SDIO signal traces with total grounding. The impedance of SDIO signal

trace is 50 Ω ±10 %.
 Keep SDIO signals far away from other sensitive circuits/signals such as RF circuits, analog signals,
etc., as well as noisy signals such as clock signals, DC-DC signals, etc.
 It is recommended to keep matching length between SDC1_CLK and SDC1_DATA[0:3]/SDC1_CMD
less than 1 mm and total routing length less than 50 mm.
Keep termination resistors within 15–24 Ω on SDC1_CLK signal traces near the module and keep

the routing distance from the module's SDC1_CLK pin to termination resistors less than 5 mm.
 Make sure the adjacent trace spacing is 2 times of the trace width and bus capacitance is less than
15 pF.

3.14.2. Bluetooth Application Interface

EC21 series module supports a dedicated UART interface and a PCM interface for Bluetooth application.
And Bluetooth functions are under development.
Further information about Bluetooth application interface will be provided in future version of this
document.

3.15. ADC Interfaces

The module provides two analog-to-digital converter (ADC) interfaces. AT+QADC=0 can be used to read
the voltage value on ADC0 pin. AT+QADC=1 can be used to read the voltage value on ADC1 pin. For
more details about these AT commands, see document [2].
To improve the accuracy of ADC, the trace of ADC should be surrounded by ground.
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