Shulou(Shulou.com)06/01 Report--

In order to let everyone fully understand the truth of UART serial communication, we first use P3.0 and P3.1 as IO ports to stop the process of imitating and practicing serial communication. After understanding the reason, we use the memory to set up equipment to complete the serial communication process.

With regard to the UART serial port baud rate, the commonly used values are 300,600,1200, 2400, 4800, 9600, 14400, 19200, 28800, 38400, 57600,115200 and so on. IO port imitates UART serial communication program is a complex demonstration program, we use serial port debugging assistant to send a data, data plus 1, and then take the initiative to go.

Serial debugging assistant, here we directly use the serial debugging assistant of STC-ISP software, first tell everyone about the use of serial debugging assistant, as shown in figure 11-6. The first step is to select the serial assistant menu, the second step is to choose hexadecimal display, the third step is to choose hexadecimal transmission, and the fourth step is to choose COM port, this COM port is different from the COM port in my computer equipment manager, the baud rate is selected according to the choice set by our program, the time for a data bit to continue in our program is 1go 9600 seconds, then the central selection baud rate is 9600, check bit N, data bit 8. Stop position 1.

Figure 11-6 Serial debugging assistant diagram

The essence of serial debugging assistant is to use the UART communication interface on the computer to send data to our single-chip microcomputer, and we can also accept the data sent by our single-chip microcomputer to this debugging assistant interface.

Due to the skills of communication for the first time, I stop the previous IO imitating serial communication program so that everyone can read my instructions while reading the program and thoroughly understand the underlying truth first.

There is no need to say the part of the variable bound, just look at the main function of main. The first is the setting of the baud rate of the communication, here we set the baud rate of the equipment is 9600, then the serial debugging assistant must also be 9600. When setting the baud rate of the equipment, we use the form of quasi-timer T0. In form 2, TH0 no longer represents the high 8 bits, TL0 represents the low 8 bits, but as long as the TL0 stops counting, when the TL0 overflows, it will not only change the TF0 to 1, but also actively load the contents of the TH0 into the TL0. Such a benefit is that we can early store the initial value of the desired timer in TH0, when TL0 overflows, TH0 takes the initiative to re-send the initial value to TL0, fully active, does not require the program to re-assign values to TL0, the method of setting equipment is very complex, everyone can take a look at the program and calculate the initial value.

The baud rate is set in the future, open the infix, and then wait for the data sent by the serial debugging assistant to be accepted. When accepting the data, first stop the low-level detection while (PIN_RXD). If there is no low level, it will clarify that there is no data. Once the low level is detected, enter the start-up acceptance function StartRXD (). The acceptance function starts half of the baud rate cycle at the beginning, but it is not clear that beginners can do it here. Everyone looks back at the serial data representation diagram in figure 11-2. If we read it when the data bit level changes, it is easy to misread the data because of timing errors and signal volatility. So we want to read the data when the signal fluctuates most. Except for the status of who the signal changes along, the other status is very volatile, so we now agree to read the level shape at both ends of the signal, so that we can guarantee that what we read must be accurate.

Once we have read the original signal, we will set the later form to the accepted form, and turn on the timer infix. The first time is after half a cycle has entered the infix, we will stop judging the original bit twice and make sure that the original bit is a low level, not a disturbing signal. From now on, enter the infix every 9600 seconds via 1max, and read the shape of the pin into the RxdBuf. After waiting for the end of the acceptance, we add 1 to the RxdBuf, and then send it through the TXD pin. The abnormal requirement is to send a cause bit first, then send 8 data bits, and then send the bit. After the end of the transmission, the program runs to while (PIN_RXD), waiting for the beginning of the second round of signal acceptance.

Plain text copy # include sbit PIN_RXD = P3 ^ 0; / accept pin definition sbit PIN_TXD = P3 ^ 1; / / send pin definition bit RxdOrTxd = 0; / / instruct later form to send bit RxdEnd = 0; / / accept end mark bit TxdEnd = 0; / / send end mark unsigned char RxdBuf = 0; / / accept buffer unsigned char TxdBuf = 0 / / send buffer void ConfigUART (unsigned int baud); void StartTXD (unsigned char dat); void StartRXD (); void main () {EA = 1; / / Open total suffix ConfigUART (9600); while (1) {/ / set the equipment installation baud rate to 9600 while (PIN_RXD); / / wait for the acceptance pin to show a low level, that is, the Zhao end position StartRXD (); / / start the acceptance while (! RxdEnd); / / wait for the acceptance completion of StartTXD (RxdBuf+1) / / after the received data is + 1, send it back to while (! TxdEnd); / / wait for the completion of sending}} / * set the serial port equipment configuration function, baud- communication baud rate * / void ConfigUART (unsigned int baud) {TMOD & = 0xF0; / / clear the control bit TMOD of T0 | = 0x02; / / set the device T0 to form 2 TH0 = 256-(11059200ig12) / baud / / calculate T0 overload value} / * start serial admission * / void StartRXD () {TL0 = 256-((256-TH0) > > 1); / / T0 on time at admission startup is half baud rate period ET0 = 1; / / enable T0 suffix TR0 = 1; / / start T0 RxdEnd = 0; / / clear zero acceptance completion mark RxdOrTxd = 0 / / set the configuration to accept} / * start serial transmission, dat- to be sent byte data * / void StartTXD (unsigned char dat) {TxdBuf = dat; / / the data to be sent is stored in the send buffer TL0 = TH0; / / the initial value of T0 count is overload value ET0 = 1; / / enable T0 suffix TR0 = 1; / / start T0 PIN_TXD = 0; / / send end bit TxdEnd = 0 / / clear zero and send end mark RxdOrTxd = 1; / / set the form to send} / * T0 suffix service function, handle serial send and receive * / void InterruptTimer0 () interrupt 1 {static unsigned char cnt = 0; / / bit accept or send count if (RxdOrTxd) {/ / Serial send disposition cnt++; if (cnt > = 1;} else if (cnt = = 9) {/ / send stop bit PIN_TXD = 1 } else {/ / send end cnt = 0; / / reset bit counter TR0 = 0; / / close T0 TxdEnd = 1; / / set send end mark}} else {/ / Serial admission disposition if (cnt = = 0) {/ / dispose if (! PIN_RXD) {/ / when the end bit is 0, clear the admission buffer and prepare the admission data bit RxdBuf = 0; cnt++ }} else {/ / interrupt acceptance TR0 = 0 when the origin bit is not 0; / / close T0} else if (cnt > = 1; / / low bit first, so when the previously accepted bit is moved to the right / / accept foot is 1, the buffer has the highest position 1, / but if it is 0, it still insists on 0 if (PIN_RXD) {RxdBuf | = 0x80;} cnt++;} else {/ abort bit disposal cnt = 0 / / reset the bit counter TR0 = 0; / / close the T0 if (PIN_RXD) {/ / abort bit to 1 before the data is invalid RxdEnd = 1; / / set the acceptance mark}

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