Sim800 hardware design v1.05

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Figure 28: RI behaviour of URC or receive SMS
However, if the module is used as caller, the RI will remain high. Please refer to the following figure.
HIGH
LOW
Idle
Ring
Establish
the call
Hang up
the call
Idle
RI
Figure 29: RI behaviour as a caller
4.7. Audio Interfaces
SIM800 provides one analog input, which could be used for electret microphone. The module also provides one
analog output. The output can directly drive 32 receiver.
Table 13: Audio interface definition
Pin name Pin number Function
MICP 19 Main Audio input positive
MICN 20 Main Audio input negative
SPKP 21 Main Audio output positive
Audio
channel
SPKN 22 Main Audio output negative
“AT+CMIC” is used to adjust the input gain level of microphone. “AT+SIDET” is used to set the side-tone
level. In addition, “AT+CLVL” is used to adjust the output gain level. For more details, please refer to
document [1]
In order to improve audio performance, the following reference circuits are recommended. The audio signals
have to be layout according to differential signal layout rules as shown in following figures.
SIM800_Hardware Design_V1.05 35 2014-03-25