Ri Behavior - SIM Tech SimCom SIM7100 Hardware Design

The SIM7100 UART is 1.8V interface. A level shifter should be used if user's application is equipped with
a 3.3V UART interface. The level shifter TXB0108RGYR provided by Texas Instruments is recommended.
The reference design of the TXB0108RGYR is in the following figures.
MODULE
UART port
To comply with RS-232-C protocol, the RS-232-C level shifter chip should be used to connect SIM7100 to
the RS-232-C interface. In this connection, the TTL level and RS-232-C level are converted mutually.
SIMCom recommends that user uses the SP3238ECA chip with a full modem. For more information
please refers to the RS-232-C chip datasheet.
Note: SIM7100 supports the baud rate: 300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200,
230400, 460800, 921600, 3200000, 3686400, 4000000bps. Default rate is 115200bps.
3.3.2

RI Behavior

If UART port is used in Null Modem, the pin "RI" can be used as an interrupt signal to HOST. Normally it
will keep high logic level until certain condition such as receiving SMS, voice call (CSD, video) or URC
reporting, then "RI" will change to low logic level to inform the master (client PC). It will stay low until
the master clears the interrupt event with AT command.
If Full Modem is used to establish communication between devices, the pin "RI" is another operation
SIM7100_Hardware Design_V1.01
VDD_1V8 or
External 1V8
100nF
TXD
RXD
RTS
CTS
DTR
DCD
RI
47K
Figure 17: Reference circuit of level shift
Figure 18: RI behaviour in NULL Modem
Smart Machine Smart Decision
3.3V
TXB0108RGYR
100nF
VCCA VCCB
OE
GND
B1
A1
A2 B2
A3 B3
A4 B4
A5 B5
A6 B6
B7
A7
47K
A8 B8
32
TXD_3.3V
RXD_3.3V
RTS_3.3V
CTS_3.3V
DTR_3.3V
DCD_3.3V
RI_3.3V
2015-01-20