1. Introduction
Along with the correspondence enterprise’s development, the mobile communication application domain’s unceasing expansion, mobile termination’s design gradually time is also paid attention. This article introduced Siemens Corporation’s GSM in detail module TC35, TI Corporation’s components and so on level switch chip MAX3238, and constitution mobile termination hardware circuit. This design may complete short news receiving and dispatching, the speech transmission, to carry on functions and so on data transmission with PC machine, has applied in based on GSM in the short news GPS vehicles supervisory system.
2. TC35 module
TC35 is the new generation wireless communication GSM module which Siemens Corporation promotes, may the fast security realize in the system plan data, the speech transmission, the short news service reliably (Short Message Service) and the facsimile. The module working voltage is 3.3 - 5.5V, may work in 900MHz and the 1800MHz two frequency bands, in the frequency band power loss respectively is 2W (900M) and 1W (1800M). The module has at order collection connection, supports the text and the PDU pattern short news, the third group of two kind of facsimile, as well as the 2.4k,4.8k,9.6k opaque pattern. In addition, this module also has the telephone directory function, the multi-party, the roaming measuring ability, the commonly used working pattern has province patterns and so on electricity pattern, IDLE, TALK. Through the unique 40 pin’s ZIF coupling, realizes the power source connection, the instruction, the data, the voice signal, and the control signal two-way transmission. Through the ZIF coupling and 50Ω the antenna coupling, may connect the SIM card support and the antenna separately.
The TC35 module mainly by the GSM baseband processor, the GSM radio frequency module, power supply module (ASIC), dodges saves, the ZIF coupling, the antenna connection six parts to be composed. As the TC35 core, the baseband processor mainly processes in the GSM terminal the pronunciation, the data signal, and has covered in honeycomb radio frequency equipment’s all simulations and the digital function. In does not need under the extra hardware circuit’s premise, may support FR, HR and the EFR pronunciation channel coding.
Figure 1 TC35 function diagram
3. Periphery using electric circuit
The TC35 module’s normal operation needs the corresponding peripheral circuit and its coordination. TC35 altogether has 40 pins, through the ZIF coupling separately with power circuit, start and close-down electric circuit, data communication electric circuit, connections and so on voice communication electric circuit, SIM card electric circuit, indicating lamp electric circuit. As shown in Figure 2,
Figure 2 TC35 peripheral circuit connection
3.1 power sources and starting circuit
The power circuit divides into the rechargeable battery and the voltage-stabilized source module two parts: The rechargeable battery mainly provides the 3.6V work electricity voltage for the overall system, simultaneously has the high level which MAX3238 needs; TI Corporation’s three end power source module UA7806 the exterior 12V direct-current power supply transformation is 6V, including arrives at the ZIF coupling 11, 12 pins, in charges under the pattern, is TC35 provides 6V, the 500mA charging voltage.
The starting circuit by operates the drain electrode triode and the previous electricity reset circuit is composed. After module electricity 10ms, (battery voltage must be bigger than 3V), to cause it normal work, must (/IGT) overtime long in 15 feet is the 100ms low level signal at least, and this signal drops along the time is smaller than 1ms. After the start, 15 foot’s signals should maintain the high levels. The next chart shows, produces the signal for the starting circuit, may see 10ms the time delay and the 100ms low level.
Figure 3 gathers the start signal falls along
3.2 data communication electric circuit
The data communication electric circuit mainly completes short news receiving and dispatching, and the PC machine correspondence, functions and so on software class control. The TC35 data interface uses serial asynchronous receiving and dispatching, conforms to ITU-T the RS-232 interface circuit standard, works in the CMOS level (2.65V). The data interface disposition is 8 bit data positions, 1 stop position, does not have the verification position, may move, the automatic baudrate which under the 300bps~115kbps baudrate supports is 4.8kbps~115kbps (14.4kbps and the 28.8kbps exception). The TC35 module also supports RTS0/CTS0 the hardware handshake and the XON/XOFF software class control.
The data communication electric circuit take TI Corporation’s MAX3238 chip as a core, realizes the level switch and the serial port correspondence function.
TI Corporation’s MAX3238 chip power line voltage is 3~5.5V, conforms to TIA/EIA-232-F and ITU the v.28 standard. Has the unique ±15KV human body static electricity protective measures, the compatible 5V logic input, contains 3 groups receives, 5 group transmission serial communication connections, the maximum data transfer rate may reach 250 kbps. This chip’s most major characteristic is, in the serial port non-data feeds’s situation, may nimble carry on the power source management, namely, when FORCEON (13 feet) are the low level, /FORCEOFF (14 feet) are the high levels, Auto-Powerdown the Plus function is effective. Under normal operation pattern, in approximately 30 second event, if the chip is receiving and the transmission pin has not examined the desired signal, will enter the Powerdown pattern automatically, this time consumes electricity 1uA. If FORCEON and the /FORCEOFF pin is the high level, then Auto-Powerdown Plus malfunction. When Auto-Powerdown Plus function effective, if examines the receive or the transmission pin has the signal input, this chip is activated automatically, returning to normal active status. If any reception channel’s input voltage is higher than 2.7V or is smaller than - 2.7V, or is located at - the 0.3V~0.3V time is smaller than 30uS, then /INVALID (15 feet) pin for high level (data effective). If all reception channel’s input voltage is bigger than 30uS located at - the 0.3V~0.3V time, then /INVALID (15 feet) pin for low level (data invalid).
Table 1 output control truth table
This chip’s above characteristic, satisfied TC35 to take the mobile termination 3 groups receives, 5 group transmission electric circuit connection request. When MAX3238 and ZIF coupling corresponding pin connection, must pay attention to the transmission, the receive pin connection to be correct. MAX3238 also needs to connect 4 0.1uF the electric capacity coordinations, can complete the level switch function. The TC35 module has RxD0, CTS0, DSR0, DCD0, RING0 through the RS-232 connection various pins output’s signal, the input signal is TxD0, RTS0, DTR0.
Because the TC35 interface circuit has used 9 needle serial port complete pin, enables TC35 to be possible to obtain DTR0, DSR0, DCD0 and the RING0 control signal. Signal RING0 uses for to the honeycomb equipment to instruct that receives Unsolicited Result Code (URC). Through at instruction, may establish TC35 the different movement pattern.
3.3 voice communication electric circuit
Because in the TC35 GSM baseband processor integrated parts and so on audio frequency filter, ADC, DAC, speech synthesis, therefore the module pronunciation connection’s peripheral circuit connection is relatively simple. TC35 has two pronunciation connections, each connection has simulates Mike to input and the simulation earphone outputs. In order to suit the different peripheral device, the module altogether has 6 kind of speech patterns, may through the instruction AT^SNFS choice. The first pronunciation connection’s default disposition is Votronic the HH-SI-30.3/V1.1/0 hand-hold microphone, the speech pattern is 1 (default), 4, 5, the pattern 1 parameter is fixed. The second pronunciation connection wears the type earphone and Mike for establishes, the speech pattern is 2, 3, 6.
In order to prevent from the microphone and the earphone wire introduction high frequency interference, affects TC35 the normal operation. When designa circuit, in the microphone, the earphone, as well as the hand-hold receiver’s jack place meets has the inductance. In addition, considered the static electricity protection the factor, all voice signal input end passes the electric capacity and the GND coupling.
3.4 SIM card electric circuit
The baseband processor integrated one with ISO 7816-3 IC Card the standard compatible SIM connection. In order to suit the exterior SIM connection, this connection connects the main interface (the ZIF coupling). In GSM11.11 is the SIM card reserves 5 pins in the foundations, TC35 was the SIM card connection has reserved 6 pins on the ZIF coupling, increased the CCIN pin used for to examine in the SIM card support whether to insert has the SIM card. When inserts the SIM card, this pin sets for the high level, the system only then enters the normal work condition. But present moves the SIM card which the operator provides not to have the CCIN pin, therefore in designa circuit time is connected pin CCIN and CCVCC.
When the design is the SIM card wiring, had discovered is worth causing the attention question: If is directly connected SIM card fourth foot CCGND with printed wiring board’s GND, does not make any signal the isolation protection, then talks over the telephone time the volume is very small. Considers in the design factors and so on electromagnetic compatibility and static electricity protection, to achieve the best telephone conversation effect, uses under the SIM support, namely printed wiring board’s top layer lays a copper isolation network, this level spreads the copper and SIM the card CCGND pin is connected, CCGND and between circuit wafer GND passes two parallel electric capacities and the inductive couplings. This act was the SIM card constituted isolation place, has shielded other holding wires to the SIM card disturbance. When again carries on the pronunciation telephone conversation, the voice is clear.
4. Concluding remark
Mobile termination which and the peripheral circuit constitutes by Siemens Corporation’s GSM module TC35, may very good complete short news receiving and dispatching, the data and the voice communication. This mobile termination unifies Rockwell Corporation’s Jupiter GPS the OEM board, and Che Zai who is composed of the monolithic integrated circuit control moves the unit, may very good complete uses the GSM short message passing vehicles localization information the work.
Reference
1 Siemens TC35/TC37 Hardware Interface Description Vision 04.00, 2002.5.29
2 Cellular Engine TC35 Audio Interface Vision 02.00, 2001.11.21
3 GSM11.11 Vision 6.2.0, 1999.5
