GSM/GPRS Module
M85 Hardware Design
M85_Hardware_Design Confidential / Released 44 / 92
As to the circuit below, VDD_EXT supplies power for the I/O of module, while VCC_MCU supplies power
for the I/O of the peripheral.
Peripheral
/TXD
/RXD
VDD_EXT
4.7K
VCC_MCU
4.7K
5.6K
4.7K
VDD_EXT
TXD
RXD
RTS
CTS
DTR
RI
/RTS
/CTS
GND
GPIO
DCD
Module
GPIO
EINT
VCC_MCU
Voltage level: 5V
4.7K
GND
Figure 25: Level Match Design for 5V System
The following circuit shows a reference design for the communication between module and PC. Since the
electrical level of module is 2.8V, so a RS-232 level shifter must be used.
9
8
7
6
5
4
3
2
1
15
14
8
9
11
12
5
7
6
10
4
26
2
27
13
18
20
21
16
17
19
22
23
24
3
1
25
28
GND
TO PC serial port
SP3238
3V
GND
GND
T5OUT
/SHUTDOWN
V+
GND
V-
VCC
T4OUT
T2OUT
T3OUT
T1OUT
R3IN
R2IN
R1IN
/STATUS
3V
ONLINE
R1OUT
R2OUT
R3OUT
/R1OUT
GND
T5IN
T4IN
T3IN
T2IN
T1IN
C2+
C2-
C1-
C1+
Module
RXD
DTR
RTS
RI
CTS
TXD
DCD
Figure 26: Level Match Design for RS-232
Quectel
Confidential