It is to STR912FW44X6 chip as MCU hardware development platform, STR912FW44X6 expansion outside the dot matrix LCD display, input keys, UART interfaces, IrDA, CAN, USB, ETM interface, audio amplifier / microphone amplifier and Ethernet interfaces. Of these, UART interface and Ethernet interface as used herein. UART interface into a RS232 serial port and two RS485 serial port. RS232 serial port for the GSM module connected to the RS232 serial port to enable GPRS wireless transmission, two RS485 serial ports, one used as a MODBUS communication interface used to access another meter gauge to collect statistics and display generating capacity of solar power systems. Ethernet connection to the network through the network cable, to enable wireless transmission of data.

1. RS232 serial circuit design and functions to achieve

RS232 is a serial data interface standard, is the most common serial interface standard for data transmission between a computer and computer, computer and peripherals. RS 232 serial interface bus for communications distance between the devices is not more than 15m, transfer rates of up to 20 KB / s.

RS232 serial port is produced by ST’s ST3232EAR to achieve. ST3232EAR is a kind of the computer’s serial port RS 232 signal level (-lO V, + 10 V) is converted to the microcontroller used by the TTL signal level (OV, + 3.3 V) chips. Its internal structure consists of three parts: The first part is a charge pump circuit, composed of 1 to 6 feet and 4 capacitor. Its function is to produce two +12 V and -12 V power supply for the RS 232 serial port to provide the level of need. The second part is the data conversion channel from 7 to 14 feet constitute two data channels. Among them, 13 feet (RlIN), 12 feet (R1OUT), 11 feet (TlIN), 14 feet (T1OUT) for the first data channel; 8 feet (R2IN), 9 feet (R2OUT), 10 feet (T2IN), 7 feet (T2OUT) for the second data channel. TTL / CMOS data from TlIN, T2IN input is converted to RS232 data to the computer DP9 plug from T1OUT, T20UT; after DP9 plug RS 232 data from RlIN, R2IN input is converted into TTL / CMOS data, from R1OUT, R2OUT output. The third part is powered by 15 feet GND, 16 pin VCC (+5 V) composition.

By the MCU GPIO RXD and TXD respectively ST3232 12 feet (R1OUT) and 11 feet (T1IN) is connected, so 14 feet (T10UT) and 13 feet (R1IN) output RS232 level, and then connect the GSM module RS232 serial port and serial port MCU board, you can write to the RS232 interface AT commands to achieve the purpose of controlling GSM module functions to achieve data transmission via GPRS.

2. RS485 serial circuit design and functions to achieve

RS485 is used to collect solar power system data RS485 has been adopted here instead of using the RS232, RS485 because more than RS232 has many advantages. RS232 take unbalanced transmission mode, namely single-ended communication, its receiving end of a data signal is a signal with respect to ground. So it’s common-mode rejection ability, coupled with the distributed capacitance twisted pair, maximum transmission distance of about 15 m, the highest rate of 20 KB / s, and it can only support point to point communications. The RS485 balanced send and differential accepted way to communicate, since the transmission lines are usually using twisted, sometimes differential transmission, so there is a strong resistance to common mode interference, high sensitivity bus transceiver can be detected up to 200mV of voltage, so the transmission signal in kilometers above can be restored. RS maximum communication distance of approximately 485 1219 m, maximum transfer rate of 10 MB / s, which uses dual part-work, can support multi-point data communications, the bus generally supports up to 32 nodes.

RS485 interface chip is ADM3485. ADM3485 single +3.3 V power supply work, half-duplex communication, to be completed by the TTL level to RS485 level functions. ADM34185 chip and pin are very simple structure, containing an internal drive and a receiver, the input RO and DI ended output and drives respectively receiver, simply connect with the microcontroller, respectively RXD and TXD and SCM connected to. RE and DE-were to receive and transmit enable terminal.