WM620 Hardware User Guide
V1.1
All rights reserved by Shenzhen Neoway Technology Co., Ltd.
Page 12
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.
