Smart phone terminal design

Intelligent Telephone Design

TONG Guoxiang, SUN Guoqiang, FU Yinghua

(Institute of Computer Engineering, University of Shanghai for Scienc e
And Technology, Shanghai 200093, China)

Key words: intelligent telephone; MODEM; information processing

1 system hardware function realization system block diagram shown in Figure 1. The core of the system is the main control module, which is mainly composed of a microprocessor to control the operation of the whole system software and hardware. On one hand, it processes the control information of each part of the peripheral circuit, on the other hand, it completes the intelligent processing of receiving and transmitting information, and its function is scalable, and further preserves the software interface for future functions; the storage module includes external RAM and EPROM memory. And the corresponding power-down protection circuit is used for storing data that needs to be processed and exchanged during system operation, and is also used for storing received or transmitted data information; EPROM is mainly used for storing system software and storing Chinese character fonts; keyboard input The module is configured to receive input data from a user, including control information and data information, which is an input interface of the user to the system; the LCD module is composed of an LCD display and related control circuits, and can display Chinese, English, numbers and various characters. It is the output interface of the system to the user. The MODEM module consists of an embedded MODEM chip and related peripheral circuits. On the one hand, it is used to modulate the data sent by the main control module, convert the digital information into an analog signal, and send it to the front-end telephone interface module DAA circuit; on the other hand, convert the analog signal received by the DAA circuit into a digital signal, and hand it to the main The control module is further processed. It is the import and export of all information and plays a vital role.

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The protocol can be divided into three layers: the physical layer, the link layer, and the message layer.
(1) The physical layer is responsible for the transfer of physical data bit streams between entities. In this system, the Z02215 MODEM chip is used as a modem for data transmission and reception. The chip is powerful, so the peripheral circuit is extremely simple. Z02215 is Zilog's newly developed single-chip embedded MODEM chip with integrated controller, data pump and analog front end, running on the public switched telephone network (PSTN). Z02215 is applicable to V.22bis, V.22, V. .23 (Ninitel), V.21, Bell 212A, Bell 202, Bell 202T and Bell 103 and other MODEM standards [1], [2]. The Z02215 offers comprehensive, selectable and programmable voice generation and detection. Fully meet the hardware requirements of physical layer data transmission.
(2) The link layer will provide a reliable data transmission mechanism [3]. The functions to be realized include: establishment of telephone voice path and message communication path, caller ID, packing when message is sent, unpacking function when receiving data, data check, retransmission control, and the like. The following is a packet format and communication protocol established to ensure that data is reliably transmitted and received.
Frame format: word interval + start bit + data (8 bits, send high bit after transmitting low bit first) + odd check word interval: ≥ 2bit, fixed to 1; start bit: 1 bit, fixed to 0; data: 1 byte (8 bits); odd parity: 1 bit.
Packet format: data (16bytes) + serial number (1byte) + check (1byte).
Data: If the data length is less than 16 bytes, it is filled with 0x20; serial number: adopts continuous accumulation, from 1~255, can't be 0; check digit: all data and serial number are added (excluding checksum The complement itself is checked; the receiver checks the check digit; if all the data are added equal to 0 (including the check digit) then the check is correct.
Packet confirmation information format (1 byte):
FFH: Correct reception as an acknowledgment signal; 00H: Error reception as a retransmission signal.
The half-duplex transmission mode is used, and both uplink and downlink use 1200 bps. In addition, in order to ensure reliable transmission of data, a minimum of 1 ms of 10 ms is transmitted as a synchronization code before each data packet is transmitted.
(3) The message layer specifies the format of the message and the command and the format of the confirmation message. The data sent by the upper layer is a 16-byte data packet. The sender program is responsible for increasing the serial number and verification, and the receiving program is responsible for checking the serial number and verification. The underlying program ensures the correctness and order of the submitted packets.
Transmitter: After sending a complete packet (a total of 18 bytes), the sender waits for 150ms. If no acknowledgment signal is received or a retransmission signal is received, the packet will be resent. If the acknowledgment signal is received, the next packet is sent immediately.
Receiver: If a complete data packet is not received within 200ms after receiving the first valid data, or the verification error occurs, the receiving end sends an error message, if the serial number of the received data packet and the previous data If the serial number of the packet is the same, the packet is discarded.
Receiver check: The receiver has two kinds of checksums to ensure the correct data: one is the odd check in each byte to ensure the correctness of a single byte; the other is the packet check to ensure the integrity of the whole package. Sex.
The sender retransmits: If the acknowledgment signal is still not received after the transmission is repeated three times according to the above sending process, the communication is considered to be unsuccessful, and the message that the transmission fails is reported to the upper layer and submitted to the upper layer for processing.

The core of the telephone terminal is the MCS-89C52 microprocessor. Normally, the microprocessor works in a low-power mode. When a key is pressed, it exits the low-power mode and enters the main menu. In the main menu, the user can select an action. To reduce redundant code, the software is written in assembly language, the font is solidified in an externally extended EPROM, and the internal EPROM is stored. Figure 2 shows the main program flow.