Neo_M660A GPRS Module Hardware User Guide
Copyright © Neoway Technology Co., Ltd
17
Figure 3-13
Recommended communication circuit between 3.3V MCU and UART
VDD_EXT
0.1 uF
47K
RB521S
200 Ω
33 pF
33 pF
MCU_UTXD
MCU_URXD
Module_URXD
Module_UTXD
In Figure 3-13, 100 pF filter capacitor should be placed near the receive pin of the module. Resistor (200 Ω
to 470 Ω) and capacitor (100 pF to 470 pF) can be selected based on the tested signal wave. Great serial
resistance and filter capacity will decrease the signal level significantly, resulting in undesired signal wave
distortion and the low adaptable UART communication baudrate. RB521S-30TE-61, RB521SM-30GJT2R,
and LRB521S-30T1G are recommended for separating diode.
When the external MCU adopts 5 V IO system, level shifting is required for both UART receive and
transmit. Figure 3-14 shows a reference circuit design.
Figure 3-14
Recommended communication circuit between 5V MCU and UART
OUTPUT
VCC_IN
VDD_EXT
4.7K
10K
INPUT