Ri And Dtr Behavior - SimCom SIM7000 Hardware Design

Table 11: UART electronic characteristic
Symbol Description
V UART input high level voltage
IH
V UART input low level voltage
IL
V UART output high level voltage
OH
V UART output low level voltage
OL
The SIM7000 UART is 1.8V voltage interface. If user's UART application circuit is 3.3V voltage
interface, the level shifter circuits should be used for voltage matching. The following figure shows
the voltage matching reference design.
MODULE
UART
Note: When it uses the level shifter IC, the pull up resistance on TXD_3.3V, RTS_3.3V,
DCD_3.3V and RI_3.3V should not be less than 47K
3.3.2

RI and DTR Behavior

The RI pin description:
The RI pin can be used to interrupt output signal to inform the host controller such as application
CPU. Before that, users must use AT command "AT+CFGRI=1" to enable this function.
Normally RI will keep high level until certain conditions such as receiving SMS, or a URC report
coming, then it will output a low level pulse 120ms, in the end, it will become high level.
RI
Idle
HIGH
LOW
Figure 16: RI behaviour（SMS and URC report）
The DTR pin description:
After setting the AT command "AT+CSCLK=1", and then pulling up the DTR pin, SIM7000 will
SIM7000 _Hardware Design _V1.04
VDD _ EXT
100nF
TXD
RXD
RTS
CTS
DTR
DCD
RI
47K
Figure 15: Reference circuit of level shift
120ms
Receiving SMS and any URC
report coming
Smart Machine Smart Decision
Min.
1.17
-0.3
1.35
0
3.3V
TXB0108 RGYR
100nF
VCCA VCCB
OE
GND
B1
A1
B2
A2
B3
A3
A4 B4
B5
A5
B6
A6
A7 B7
47K
A8 B8
.
Ω
Typ. Max. Unit
1.8 2.1 V
0 0.63 V
1.8 1.8 V
0 0.45 V
TXD _3.3V
RXD _3.3V
RTS _3.3V
CTS _3.3V
DTR _3.3V
DCD _3.3V
RI_3.3V
2018-1-31