How to receive multiple bytes using the hardware usart in the PIC18F2550
Hi all,
I am trying to setup a RF connection between a PC and a PIC using the MaxStream ZigBee modules. If i send a single byte from the PC to the PIC everything is ok but how do I send more then one?
I am using hardware interrupts for the USART and the USART itself only has a 1 byte buffer.
I need a way to capture 10 bytes with the PIC into a buffer array and then process it afterwards.
Last edited by PJALM; - 3rd July 2007 at 20:57.
HSERIN uses the hardware UART, but uses it in a way that's more like the bit-banged method of SERIN. Use the STR modifier to get 10 bytes into an array.Originally Posted by PJALM
Thanks for the advise but at the time of interrupt there is only one byte to get because the buffer is only one byte in size.
I need a way to capture the data one byte at a time and put each byte into the array as it arrives. This means I need to track which byte I am on and know when to start capturing and when to stop.
I will put up some sample code I made to give you an idea of what I am trying to achieve.
Ok here is a snippet from the code i am working on.
Maybe this will trigger some ideas.
Code:DEFINE OSC 48 DEFINE LOADER_USED 1 DEFINE RESET_ORG 800h ' For Microchip USB Bootloader DEFINE INTERRUPT_ORG 808h ' For Microchip USB Bootloader '------------------------------------------------------------------------------- ' System Settings '------------------------------------------------------------------------------- ADCON1 = 15 ' Set all I/Os to Digital INTCON2.7 = 1 ' Disable PortB Pullups CMCON = 7 ' Disable Comparators My_Address VAR BYTE i VAR BYTE ii VAR WORD i = 0 ii = 0 My_Address = 0 '------------------------------------------------------------------------------- '------------------------------------------------------------------------------- ' RF Settings '------------------------------------------------------------------------------- DEFINE HSER_BAUD 9600 DEFINE HSER_RCSTA 90h DEFINE HSER_TXSTA 20h 'DEFINE HSER_SPBRG 25 DEFINE HSER_CLROERR 1 RF_ACK CON $01 ' Expected acknowledge char from RS-485 RF_STX CON $02 ' Start of Transmission Byte RF_ETX CON $03 ' End of Transmission Byte RF_POS CON $04 RF_To_Address VAR BYTE RF_From_Address VAR BYTE RF_Command VAR BYTE RF_Parameter VAR WORD RF_Data VAR BYTE RF_Buffer VAR BYTE[7] RF_Bytes_Sent VAR BYTE RF_Bytes_Received VAR BYTE RF_Sending_Data VAR BIT RF_Receiving_Data VAR BIT RF_Send VAR BIT RF_ACK_Received VAR BIT RF_PPP_Received VAR BIT RF_POS_Received VAR BIT RF_B0 VAR BYTE RF_B1 VAR BYTE RF_To_Address = 0 RF_From_Address = 0 RF_Command = 0 RF_Parameter = 0 RF_Send = 0 RF_Bytes_Received = 0 RF_Receiving_Data = 0 RF_ACK_Received = 0 RF_PPP_Received = 0 RF_POS_Received = 0 RF_B0 = 0 RF_B1 = 0 '------------------------------------------------------------------------------- '------------------------------------------------------------------------------- ' Interrupt Settings '------------------------------------------------------------------------------- INTCON.6 = 1 ' Enable Peripheral Interrupts INTCON.7 = 1 ' Enable Global Interrupt Handler PIE1.4 = 0 ' Disable USART Transmit Interrupt PIE1.5 = 1 ' Enable USART Receive Interrupt '------------------------------------------------------------------------------- PAUSE 500 My_Address = 18 ON INTERRUPT GOTO Main_Interrupt_Handler ENABLE INTERRUPT '------------------------------------------------------------------------------- ' Main Program Loop '------------------------------------------------------------------------------- MainLoop: GOSUB Get_My_Address 'IF RF_Receiving_Data = 0 THEN ' IF RF_Command != 0 THEN ' IF RF_To_Address = My_Address THEN ' GOSUB RF_Process_Command ' ENDIF ' ENDIF 'ENDIF PAUSE 50 GOTO MainLoop '------------------------------------------------------------------------------- '------------------------------------------------------------------------------- ' Send RF data '------------------------------------------------------------------------------- RF_Send_Data: RF_From_Address = My_Address RF_Ack_Received = 0 RF_PPP_Received = 0 RF_Buffer(1) = RF_STX 'Start RF_Buffer(2) = RF_To_Address + 4 'To Address RF_Buffer(3) = RF_Command 'Command RF_Buffer(4) = RF_Parameter.HighByte + 4 'Parameter High Byte RF_Buffer(5) = RF_Parameter.lowbyte + 4 'Parameter Low Byte RF_Buffer(6) = RF_From_Address + 4 'From Address RF_Buffer(7) = RF_ETX 'End FOR i = 1 TO 25 PAUSE 10 NEXT FOR i = 1 to 7 RF_Data = RF_Buffer(i) HSEROUT [RF_Data] 'Send the Data Byte PAUSE 25 NEXT FOR i = 1 TO 25 PAUSE 10 NEXT FOR i = 1 TO 7 RF_Buffer(i) = 0 NEXT RF_To_Address = 0 RF_From_Address = 0 RF_Command = 0 RF_Parameter = 0 RETURN '------------------------------------------------------------------------------- '------------------------------------------------------------------------------- ' Interrupt Handler '------------------------------------------------------------------------------- DISABLE INTERRUPT ' No interrupts past this point Main_Interrupt_Handler: '--------------------------------------------------------------------------- ' USART Receive Interrupt '--------------------------------------------------------------------------- IF PIR1.5 = 1 THEN PAUSE 50 HSERIN [RF_B0] SELECT CASE RF_B0 CASE RF_STX RF_Bytes_Received = 1 RF_Receiving_Data = 1 RF_Bytes_Received = 0 FOR i = 2 TO 7 RF_Buffer[i] = 0 NEXT RF_Bytes_Received = RF_Bytes_Received + 1 RF_Buffer(RF_Bytes_Received) = RF_B0 CASE RF_ETX RF_Bytes_Received = RS485_Bytes_Received + 1 RF_Buffer(RF_Bytes_Received) = RF_B0 RF_Receiving_Data = 0 RF_To_Address = RF_Buffer(2) - 4 RF_Command = RF_Buffer(3) - 4 RF_Parameter.HighByte = RF_Buffer(4) - 4 RF_Parameter.LowByte = RF_Buffer(5) - 4 RF_From_Address = RF_Buffer(6) - 4 CASE ELSE IF RF_Receiving_Data = 1 THEN RF_Bytes_Received = RF_Bytes_Received + 1 RF_Buffer(RF_Bytes_Received) = RF_B0 ENDIF END SELECT PIR1.5 = 0 ENDIF '--------------------------------------------------------------------------- '--------------------------------------------------------------------------- ' USB Interrupt '--------------------------------------------------------------------------- IF PIR2.5 = 1 THEN DEBUG 13, 10, "[ INTERRUPT ] USB Interrupt", 13, 10 PIR2.5 = 0 ENDIF '--------------------------------------------------------------------------- IntDone: RESUME ' Return to main program ENABLE INTERRUPT '------------------------------------------------------------------------------- END
Has anyone had any luck with this code yet or hav any sugestions?
Has anyone at all had any experience with this? I still cannot successfully receive more then 1 byte without problems. ANy help at all would be greatly apreciated.
Thanks
When using ON INTERRUPT the interrupts don't get handled until the currently executing PBP statement has finished.
At 9600 baud it only takes 1.04ms per byte. With the USARTS 2 byte buffer, the longest that any statement can take is 2.08ms. Anything taking longer will cause the buffer to overflow. Then with [DEFINE HSER_CLROERR 1] the program never even knows it lost data.
With PAUSE 50 in the MainLoop, you could easily loose 15-20 bytes at a time.
If you were using ASM interrupts, that wouldn't be a problem.
HTH,
DT
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