1 Introduction
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With the development of inertial navigation technology, the inertial navigation system needs to receive more RS-232, RS-422, and RS-485 serial signals from GPS, Beidou Double Star, and Elevation. In this way, the original serial channel of the inertial navigation system is not enough to receive so many serial port signals, so serial port expansion is required. The asynchronous transceiver TL16C554 chip produced by Ti Company is a good choice for serial port expansion. It has four channels and can communicate with four serial signals, which solves the problem of the shortage of serial signal interface of the original inertial navigation system. Each channel has two 16-byte FIFO (First In First Out) buffers, one for receiving data and the other for data to be sent. When operating in the FIFO mode, it is not necessary to generate an interrupt every time a frame of data is received or transmitted, thereby reducing the number of times the interrupt occurs and improving the efficiency and reliability of receiving and transmitting the serial signal.
A brief introduction to each part of the vehicle navigation is as follows:
Path guidance: guide the user along the planned path;
Man-machine interface: Provides a friendly interface that allows users to interact with the system;
Wireless communication module: allows users to exchange information with the monitoring center and other departments in real time;
Electronic map database: contains digital map information stored in a predetermined format, which is a software platform of the system;
Map matching module: determining the location of the vehicle on the map through an appropriate matching and identification process;
Path planning: help drivers plan routes based on map database and real-time location information;
Positioning module: Position the vehicle by means of GPS, inertial navigation system or mobile communication.
2 main features
The main features of the TL16C554 are as follows:
ç»„æˆ consists of four TL16C550 asynchronous communication units with logic control;
波特Up to 1M baud rate with programmable baud rate generator for flexible selection of data transceiving frequency;
î—¹ has a 16-byte transceiver FIFO buffer;
î—¹ has independently controllable transmit, receive, line status and MODEM status interrupts;
î—¹With full-duplex receiving and transmitting lines, it can independently receive and send control;
î—¹ Comprehensive line status reporting function;
î—¹ Fully categorized interrupt system control;
î—¹ Three-state TTL level output.
3 internal structure and working principle
The four-channel asynchronous transceiver integrated chip TL16C554 is available in 64-pin TQFP and 68-pin PLCC packages. The 68-pin PLCC package supports 68 (Motorola) mode. Therefore, it can be easily interconnected with Motorola microprocessor. The pin description of TL16C554 is shown in Table 1.
3.1 System I / O bus
The data lines (D0-D7) of the TL16C554 can be directly connected to the lower eight bits of the data bus of the CPU. They are the data input and output channels of the UART. The read and write operations are distinguished by the data input and output gate lines. The line can realize bidirectional communication between the UART and the CPU. The TL16C554 can also choose 16 mode (Intel bus) or 68 mode (Motorola bus). It has four serial interfaces, each with its own independent transceiver function.
3.2 clock
The reference clock of the TL16C554 can be supplied externally or internally by a crystal.
3.3 read / control logic
Communication control is implemented between the UART and the CPU through a set of signal lines including reset control RESET, chip enable, register enable interrupt request INT (AD), read data valid, and write data valid.
3.4 MODEM logic control
The MODEM control logic is mainly used to complete the interface communication between the UART and the RS-232C. These signals are driven by the EIA driver and conform to the RS-232C standard. The MODEM control logic signals include the following eight types:
RX (AD) î€ serial input, equivalent to receiving data RxD;
TX (AD) î€ serial output, equivalent to transmitting data TxD;
(AD)î€data device ready input;
(AD) î€ data terminal ready output;
(AD)î€ request to send input;
(AD)î€ clear the send input;
(AD) î€ carrier signal detection input;
(AD) î€ Ringing indicator input.
3.5 main register
The main registers in the TL16C554 are the baud rate divisor register, the line control register (LCR), the line status register (LSR), the interrupt enable register (IER), the interrupt flag register (IIR), the MODEM control register (MCR), and the MODEM status register. (MSR), Transmit Holding Register (THR), Receive Buffer Register (RHR), etc.
4 TL16C554 and microcontroller interface
In the inertial navigation system, the 80C196 MCU uses the asynchronous transceiver TL16C554 to frequently receive serial signals such as GPS, binary, and elevation meters. In addition, other tasks such as temperature control and communication with the host computer must be completed. Therefore, if the serial signal is received by the query method, it will undoubtedly waste a lot of CPU time and increase the burden on the CPU, which is obviously not feasible. The interrupt mode does not occupy CPU time. In addition, the 16-byte FIFO buffer is used to reduce the number of interrupts and improve the real-time and reliability of data reception. Therefore, the interrupt mode is selected in this system.
Experiments show that the above software and hardware design can realize reliable and timely asynchronous transceiver service of four-way serial signals, which can meet the requirements of the inertial navigation system.
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