I have this very strange problem. I am recieving data on UART and when I try to throw the data on any port, it shows up mometarily on the port and then all the port goes to zero. I do not understand this but the code works fine in debugger with SIN command.Here is the code if any one want to give a suggestion .Thanks #include "REG51CC01.h" void serial_IT(void) interrupt 4 using 2 { char uart_data=0; if (RI == 1) { RI = 0; // clear reception flag uart_data = SBUF; // Read data P2=uart_data; //Output recieve data } } void main (void) { unsigned char del=0; SCON = 0x50; /* uart in mode 1 (8 bit), REN=1 */ T2CON &= 0xF0; /* EXEN2=0; TR2=0; C/T2#=0; CP/RL2#=0; */ T2CON |= 0x30; /* RCLK = 1; TCLK=1; */ TH2=0xFF; /* init value */ TL2=0xFD; /* init value */ RCAP2H=0xFF; /* reload value, 115200 Bds at 11.059MHz */ RCAP2L=0xFD; /* reload value, 115200 Bds at 11.059MHz */ ES = 1; /* Enable serial interrupt */ EA = 1; /* Enable global interrupt */ TR2 = 1; /* Timer 2 run */ while(1); }
Thanks for your reply, Eric. Yes, I do not have any external memory. Secondly, I also thought there may be something following my first data that overwrites it so I counted the number of interrupts and there is exactly one interrupt after I send one data to UART. Now here is another strange thing, if I run this program with if statement in interrrupt routine as shown in the following program it works just fine. But I guess by using this approach I can not recieve zero on UART. #include "REG51CC01.h" void serial_IT(void) interrupt 4 using 2 { char uart_data=0; if (RI == 1) { /* if reception occur */ RI = 0; /* clear reception flag for next reception */ uart_data = SBUF; /* Read receive data */ if(uart_data) P2=uart_data; } } void main (void) { unsigned char del=0; SCON = 0x50; /* uart in mode 1 (8 bit), REN=1 */ T2CON &= 0xF0; /* EXEN2=0; TR2=0; C/T2#=0; CP/RL2#=0; */ T2CON |= 0x30; /* RCLK = 1; TCLK=1; */ TH2=0xFF; /* init value */ TL2=0xFD; /* init value */ RCAP2H=0xFF; /* reload value, 115200 Bds at 11.059MHz */ RCAP2L=0xFD; /* reload value, 115200 Bds at 11.059MHz */ ES = 1; /* Enable serial interrupt */ EA = 1; /* Enable global interrupt */ TR2 = 1; /* Timer 2 run */ while(1); }
Can you post the assembly code generated for the interrupt handler? I have a vague recollection of a couple of recent bug fixes that had to do with comparing bits and integers. What does if (RI == 1) compile into? What about if (RI) ?