Figure 27: RI behaviour of voice calling as a receiver

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Figure 29: 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. 
Figure 30: RI behaviour as a caller 
4.7. Audio Interfaces 
SIM800H&SIM800L provides two analog inputs (MIC1P/1N; MIC2P/2N), which could be used for electret 
microphone. The module also provides two analog outputs (SPK1P/1N; SPK2P/2N). 
Table 13: Audio interface definition 
 
Pin name 
Pin number 
Function 
MIC1P 
52 
Main Audio input positive 
MIC1N 
12 
Main Audio input negative 
SPK1P 
53 
Main Audio output positive 
Main 
SPK1N 
13 
Main Audio output negative 
MIC2P 
9 
Secondary Audio input positive 
MIC2N 
10 
Secondary Audio input negative 
SPK2P 
51 
Secondary Audio output positive 
Secondary 
SPK2N 
11 
Secondary Audio output negative 
SPK1P/1N output can directly drive 32Ω receiver, SIM800H&SIM800L internal has class-AB audio amplifier, 
the following table is class-AB performance: 
SIM800H&SIM800L_Hardware Design_V2.02 35 2015-07-27 

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Table 14: Performance of audio amplifier 
Conditions 
Class-AB AMP 
4.2V 8Ω THD+N=1% 
0.87W 
3.4V 8Ω THD+N=1% 
0.53W 
4.2V 8Ω THD+N=10% 
1.08W 
3.4V 8Ω THD+N=10% 
0.65W 
SPK2P/2N output can directly drive 8Ω speaker. 
AT command “AT+CMIC” is used to adjust the input gain level of microphone. AT command “AT+SIDET” 
is used to set the side-tone level. In addition, AT command “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.

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