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will be some cheep noise from speaker output easily. So it is better to put big capacitors and ferrite beads near

audio PA input.

TDD noise has something to do with GND signal. If GND plane is not good, lots of high-frequency noises will

interference microphone and speaker over bypass capacitor. So a good GND during PCB layout could avoid

TDD noise.

4.8. SIM Card Interface

The SIM interface complies with the GSM Phase 1 specification and the new GSM Phase 2+ specification for

FAST 64 kbps SIM card. Both 1.8V and 3.0V SIM card are supported. The SIM interface is powered from an

internal regulator in the module.

4.8.1.

SIM Card Application

Table 17: SIM pin definition

Pin name

Pin number

Function

SIM_VDD

Voltage supply for SIM card. Support 1.8V or 3V SIM card

SIM_DATA

SIM data input/output

SIM_CLK

SIM clock

SIM_RST

SIM reset

SIM_DET

SIM card detection

It is recommended to use an ESD protection component such as ST (www.st.com ) ESDA6V1-5W6 or ON

SEMI (www.onsemi.com ) SMF05C. That the SIM peripheral circuit should be close to the SIM card socket.

The reference circuit of the 8-pin SIM card holder is illustrated in the following figure.

SIM800H&SIM800L_Hardware Design_V2.02

2015-07-27

Module

PRESENCE

100nF

MOLEX-91228

SIM Card

22pF

VCC

GND

RST

VPP

CLK

I/O

GND

VDD_EXT

SIM_VDD

SIM_RST

SIM_CLK

SIM_DATA

4.7K

ESDA6V1

SIM_DET

51Ω

Figure 33: Reference circuit of the 8-pin SIM card holder

The SIM_DET pin is used for detection of the SIM card hot plug in. Customer can select the 8-pin SIM card

holder to implement SIM card detection function. AT command “AT+CSDT” is used to enable or disable SIM

card detection function. For details of this AT command, please refer to document [1].

If the SIM card detection function is not used, customer can keep the SIM_DET pin open. The reference circuit

of 6-pin SIM card holder is illustrated in the following figure.

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