Based on bi-directional transparent serial port extension technology for multi-parameter monitor design (1)

Embedded multi-parameter monitor systems typically include multiple independent hardware acquisition module, each hardware acquisition module completed on ECG, respiration, body, body temperature, blood pressure and blood oxygen saturation and other physiological parameters of the collection, and through its serial receive HOST-side control information, scheduled to HOST sends data acquisition.

This embedded multi-parameter monitor HOST side AT91RM9200 Processor, the processor has four universal synchronous/asynchronous receiver/transmitter (USART), one of which is the DEBUG serial port, but they are both time-multiplexed [1].

In order for HOST-side better communicate the acquisition module, you must solve their problem of serial port extension.

Now compare generic serial port expansion programme there are 2 kinds.

A hardware implementation, use the multi-serial ARM/MCU or dedicated serial expansion chips available serial port expansion chips have TI Corporation 16C55X series serial expansion chips and goldtel¡± developed GM812X series serial expansion chips, etc. TI 16C55X series chip company through the serial port, parallel port extended feature comparison strong, communication speed is high, but the control of complex, while higher prices, mainly used in the PC machine serial port expansion. Another serial port extension program software, but a software simulation serial there disadvantages: (1) the sampling frequency is low, generally can do 2 times/bit so that the correctness of the data is difficult to maintain; (2) cannot achieve high baud rate of serial communication, software simulation cannot achieve higher than General 4 800 b/s baud rate [2-3].

Whether it's using hardware or software programmes, most serial extension products mostly one-way transmission, not enough transparency [4-7].

This article in accordance with the participation of the multi-parameter monitor project needs, proposing a two-way transparent serial port extension design programme, and through the experimental validation.

1 hardware design

1.1 serial expansion module topology

In the design, the serial port expansion module to add four user devices, each user devices can and HOST side bi-directional data transfer, using time-division multiplexing technology, i.e. at any one time, up to a maximum of only one serial port and HOST-side connection, serial port expansion module for 4-channel switching/select.

The two sides through hardware and software mechanisms for arbitration. As shown in Figure 1.

　　

1.2 hardware design

Serial port expansion module mainly consists of 2 parts: AT89C2051 microcontroller and analog switch CD4052, dual 4-channel analog switch.

Serial port expansion module topology diagram as shown in Figure 2, which dotted box for serial port expansion module.