主函数

    stm.tm_year=year-1900;  stm.tm_mon=month-1;  stm.tm_mday=day;  stm.tm_hour=hour-8;  stm.tm_min=min;  stm.tm_sec=sec;  realtime.num=mktime(&stm); //....当下位机收到'b'时，向上位机发送{时间戳}if(RsBuf[0]=='b') { Send_String("{");  send_byte(realtime.character[3]);send_byte(realtime.character[2]);send_byte(realtime.character[1]);send_byte(realtime.character[0]); Send_String("}\n");RsPoint=0;} 

2.上位机（QT…）

参考
Qt获取时间戳:https://blog.csdn.net/lmhuanying1012/article/details/78016352
点击按钮，向下位机发送’b’

void MainWindow::on_pB_read_Time_clicked(){this->serial_port->write(" b");// 串口发送"b" 读取下位机时间
}

接收数据，处理得到时间戳

union
{long int num;
unsigned char character[4];
}buf;
int id=0;
static int time_flag = 0；MainWindow::MainWindow(QWidget* parent) :QMainWindow(parent), is_open_serailport(false),serial_port(new QSerialPort(this)), ui(new Ui::MainWindow)
{QObject::connect(this->serial_port, &QSerialPort::readyRead, [this]{if(!this->is_open_serailport) return;const QByteArray& info = this->serial_port->readAll();if(info.length() <= 0) return;QString rcvStr;if(this->ui->rB_rcvMode_text->isChecked()){foreach(char b , info )//数据解析{if(b == ']'&&id==4&&data_flag == 1)... //其他数据if(b == '['&&id==0)...if(data_flag == 1)...if(data_flag == 2)...if((b != ']')&&(b != '}')&&(b != '[')&&(b != '{')&&(b != '(')&&(b != ')')&&data_flag == 0&&time_flag == 0&&rom_flag == 0)rcvStr += b;if(b == '}'&&id==5&&time_flag == 1)//结束处理time_flag = 2;if(b == '{'&&id==0)//开始处理time_flag = 1;if(time_flag == 1){//数据存入数组（得到时间戳）if(id!=0)buf.character[4-id]=b;id++;}//qDebug()<<"buf == "<//处理数据（时间戳转为字符形式）QDateTime time = QDateTime::fromTime_t(buf.num);//qDebug()<<"time == "<

void MainWindow::on_pB_SetRealTime_clicked()
{// 上位机发送{yyyy/MM/dd-hh:mm:ss} 设置下位机实时时间this->serial_port->write(" {");QByteArray time;const quint64& unix_timestamp = QDateTime::currentMSecsSinceEpoch();   //获取当前时间time+=QDateTime::fromMSecsSinceEpoch(unix_timestamp).toString("yyyy/MM/dd-hh:mm:ss");//this->serial_port->write(time);//一次性发送单片机无法处理  for (int i=0;i<=20;i++) {this->serial_port->putChar(time[i]);//延时100msQTime dieTime = QTime::currentTime().addMSecs(10);while( QTime::currentTime() < dieTime )QCoreApplication::processEvents(QEventLoop::AllEvents, 100);}this->serial_port->write("}");
}

RCIF=0;//关闭其他中断
TMR1IF=0;  
RsBuf[RsPoint++]=RCREG;//校正时间if(RsBuf[0]=='{'&&RsPoint>=20) { // 下位机收到{2022/12/06-12:31:00}  year=RsBuf[1]-48;year=RsBuf[2]-48+year*10;year=RsBuf[3]-48+year*10;//year=RsBuf[3]-48;year=RsBuf[4]-48+year*10;month=RsBuf[6]-48;month=RsBuf[7]-48+month*10; day=RsBuf[9]-48;day=RsBuf[10]-48+day*10;   hour=RsBuf[12]-48;hour=RsBuf[13]-48+hour*10;min=RsBuf[15]-48;min=RsBuf[16]-48+min*10; sec=RsBuf[18]-48;sec=RsBuf[19]-48+sec*10;  timeflag=1;Send_String("Time calibration "); Send_String("successful\n");RsPoint=0;            } 
RCIF=1;//恢复其他中断
TMR1IF=1;    

        TMR1IF=0;TMR1H=0x60;// TMR1H=0x80;  1*1.25*4TMR1L=0x00;//TMR1L=0x0;realtime.num=realtime.num+5;//时间+5s

    if(timeflag==1){ stm.tm_year=year-1900;  stm.tm_mon=month-1;  stm.tm_mday=day;  stm.tm_hour=hour-8;  stm.tm_min=min;  stm.tm_sec=sec;  realtime.num=mktime(&stm); timeflag=0;   }