Shenzhen Neoway Technology WCDMA Module : User's Manual : Page 19

WM620 Hardware User Guide V1.1

Figure 2-12, Interfacing with 3.3V logic levels of MCU

If the UART is interfacing with a MCU that has 5V logic levels, general level translators are required, for both

inputs and outputs. As shown in Figure 2-13.

Figure 2-13, Interfacing with 5V logic levels of MCU

Reference components:

R2: 2K-10K. The higher rate the UART works at, the smaller value used

R3: 4.7K-10K. The higher rate the UART works at, the smaller value used

Q1: MMBT3904 or MMBT2222. High-speed transistors preferred.

Used for 5V logic -> 2.6V logic:

While this circuit used between MCU TXD and module RXD, the INPUT signal is connected to MCU TXD,

and OUTPUT connected to module RXD. VCC_IN powered from 5V and VCC_OUT powered from 2.6V

(module’s VDD_2.6V).

Used for 2.6V logic -> 5V logic:

It can be used between module TXD and MCU RXD as well, with INPUT connected to module TXD, and

OUTPUT connected to MCU RXD. VCC_IN powered from 2.6V (module’s VDD_2.6V) and VCC_OUT

powered from 5V. This applies to RING signal as well.

Note:

Avoid sparks and glitches on UART signals while the module is in a turning on procedure.

Avoid sending any data to UART during the beginning of 2 seconds after the module being turned on.