TITLE "RS232 Communications : Half Duplex : PIC16C6x/7x/8x" SUBTITLE "Software Implementation : Interrupt Driven" ;********************************************************************************************************* ; Software Implementation Of RS232 Communications Using PIC16CXX ; Half-Duplex ; ; These routines are intended to be used with PIC16C6X/7X family. These routines can be ; used with processors in the 16C6X/7X family which do not have on board Hardware Async ; Serial Port. ; MX.. ; ; Description : ; Half Duplex RS-232 Mode Is implemented in Software. ; Both Reception & Transmission are Interrupt driven ; Only 1 peripheral (RTCC) used for both transmission & reception ; RTCC is used for both timing generation (for bit transmission & bit polling) ; and Start Bit Detection in reception mode. ; This is explained in more detail in the Interrupt Subroutine. ; Programmable Baud Rate (speed depnding on Input Clock Freq.), programmable ; #of bits, Parity enable/disable, odd/even parity is implemented. ; Parity & Framing errors are detected on Reception ; ; RS-232 Parameters ; ;The RS-232 Parameters are defined as shown below: ; ; _ClkIn : Input Clock Frequency of the processor ; (NOTE : RC Clock Mode Is Not Suggested due to wide variations) ; _BaudRate : Desired Baud Rate. Any valid value can be used. ; The highest Baud Rate achievable depends on Input Clock Freq. ; 300 to 4800 Baud was tested using 4 Mhz Input Clock ; 300 to 19200 Baud was tested using 10 Mhz Input Clock ; Higher rates can be obtained using higher Input Clock Frequencies. ; Once the _BaudRate & _ClkIn are specified the program ; automatically selectes all the appropiate timings ; _DataBits : Can specify 1 to 8 Bits. ; _StopBits : Limited to 1 Stop Bit. Must set it to 1. ; _PARITY_ENABLE : Parity Enable Flag. Set it to TRUE or FALSE. If PARITY ; is used, then set it to TRUE, else FALSE. See "_ODD_PARITY" flag ; description below ; _ODD_PARITY : Set it to TRUE or FALSE. If TRUE, then ODD PARITY is used, else ; EVEN Parity Scheme is used. ; This Flag is ignored if _PARITY_ENABLE is set to FALSE. ; ; ; Usage : ; An example is given in the main program on how to Receive & Transmit Data ; In the example, the processor waits until a command is received. The command is interpreted ; as the A/D Channel Number of PIC16C71. Upon reception of a command, the desired A/D channel ; is selected and after A/D conversion, the 8 Bit A/D data is transmitted back to the Host. ; ; The RS-232 Control/Status Reg's bits are explained below : ; ; "SerialStatus" : RS-232 Status/Control Register ; ; Bit 0 : _txmtProgress (1 if transmission in progress, 0 if transmission is complete) ; After a byte is transmitted by calling "PutChar" function, the ; user's code can poll this bit to check if transmission is complete. ; This bit is reset after the STOP bit has been transmitted ; Bit 1 : _txmtEnable Set this bit to 1 on initialization to enable transmission. ; This bit can be used to Abort a transmission while the transmitter ; is in progress (i.e when _txmtProgress = 1) ; Bit 2 : _rcvProgress Indicates that the receiver is in middle of reception.It is reset when ; a byte is received. ; Bit 3 : _rcvOver This bit indicates the completion of Reception of a Byte. The user's ; code can poll this bit after calling "GetChar" function. Once "GetChar" ; function is called, this bit is 1 and is set to 0 after reception of ; a complete byte (parity bit if enabled & stop bit) ; Bit 4 : _ParityErr A 1 indicates Parity Error on Reception (for both even & odd parity) ; Bit 5 : _FrameErr A 1 indicates Framing Error On Reception ; ; Bit 6 : _unused_ Unimplemented Bit ; ; Bit 7 : _parityBit The 9 th bit of transmission or reception (status of PARITY bit ; if parity is enabled) ; ; To Transmit A Byte Of Data : ; 1) Make sure _txmtProgress & _rcvOver bits are cleared ; 2) Load TxReg with data to be transmitted ; 3) CALL PutChar function ; ; To Receive A Byte Of Data : ; 1) Make sure _txmtProgress & _rcvOver bits are cleared ; 2) CALL GetChar function ; 3) The received Byte is in TxReg after _rcvOver bit is cleared ; ; ; ; Program: RS232.ASM ; Revision Date: ; May 17,1994 Scott Fink (Rev 2) ; Corrected 7 bit and parity operation, corrected stop bit generation, corrected ; receive prescaler settings. Protected against inadvertant WDT reset. ; 1-16-97 Compatibility with MPASMWIN 1.40 ; ;********************************************************************************************************* Processor 16C71 Radix DEC EXPAND include "p16c71.inc" _ResetVector set 0x00 _IntVector set 0x04 TRUE equ 1 FALSE equ 0 ;********************************************************************************************************* ; Setup RS-232 Parameters ;********************************************************************************************************* _ClkIn equ 4000000 ; Input Clock Frequency is 4 Mhz _BaudRate set 1200 ; Baud Rate (bits per second) is 1200 _DataBits set 8 ; 8 bit data, can be 1 to 8 _StopBits set 1 ; 1 Stop Bit, 2 Stop Bits is not implemented #define _PARITY_ENABLE FALSE ; NO Parity #define _ODD_PARITY FALSE ; EVEN Parity, if Parity enabled #define _USE_RTSCTS FALSE ; NO Hardware Handshaking is Used include "rs232.h" ;********************************************************************************************************* ; ORG _ResetVector goto Start ; ORG _IntVector goto Interrupt ; ;********************************************************************************************************* ; Table Of ADCON0 Reg ; Inputs : WREG (valid values are 0 thru 3) ; Returns In WREG, ADCON0 Value, selecting the desired Channel ; ; Program Memory : 6 locations ; Cycles : 5 ; ;********************************************************************************************************* GetADCon0: andlw 0x03 ; mask off all bits except 2 LSBs (for Channel # 0, 1, 2, 3) addwf PCL, F retlw (0xC1 | (0 << 3)) ; channel 0 retlw (0xC1 | (1 << 3)) ; channel 1 retlw (0xC1 | (2 << 3)) ; channel 2 GetADCon0_End: retlw (0xC1 | (3 << 3)) ; channel 3 if( (GetADCon0 & 0xff) >= (GetADCon0_End & 0xff)) MESSG "Warning : Crossing Page Boundary in Computed Jump, Make Sure PCLATH is Loaded Correctly" endif ; ;********************************************************************************************************* ; Initialize A/D Converter ; Configure as Analog Inputs, VDD as Vref ; A/D Clock Is Internal RC Clock ; Select Channel 0 ; ; Program Memory : 6 locations ; Cycles : 7 ; ;********************************************************************************************************* InitAtoD: bsf STATUS,RP0 clrf ADCON1 bcf STATUS,RP0 movlw 0xC1 movwf ADCON0 return ; ;********************************************************************************************************* ; Main Program Loop ; ; After appropriate initilization, The main program wait for a command from RS-232 ; The command is 0, 1, 2 or 3. This command/data represents the A/D Channel Number. ; After a command is received, the appropriate A/D Channel is seleted and when conversion is ; completed the A/D Data is transmitted back to the Host. The controller now waits for a new ; command. ;********************************************************************************************************* Start: call InitSerialPort ; WaitForNextSel: if _USE_RTSCTS bcf STATUS,RP0 bcf _RTS ; ready to accept data from host endif call GetChar ; wait for a byte reception btfsc _rcvOver ; _rcvOver Gets Cleared when a Byte Is Received (in RxReg) goto $-1 ; USER can perform other jobs here, can poll _rcvOver bit ; ; A Byte is received, Select The Desired Channel & TMXT the desired A/D Channel Data ; bcf STATUS,RP0 ; make sure to select Page 0 movf RxReg,W ; WREG = Commanded Channel # (0 thru 3) call GetADCon0 ; Get ADCON0 Reg Constant from Table Lookup movwf ADCON0 ; Load ADCON0 reg, selecting the desired channel nop ; bsf ADCON0,GO_DONE ; start conversion btfsc ADCON0,GO_DONE goto $-1 ; Loop Until A/D Conversion Done movf ADRES,W movwf TxReg if _USE_RTSCTS bsf _RTS ; Half duplex mode, transmission mode, ask host not to send data btfsc _CTS ; Check CTS signal if host ready to accept data goto $-1 endif call PutChar btfsc _txmtProgress goto $-1 ; Loop Until Transmission Over, User Can Perform Other Jobs ; goto WaitForNextSel ; wait for next selection (command from Serial Port) ; ;********************************************************************************************************* ; RS-232 Routines ;;********************************************************************************************************* ; Interrupt Service Routine ; ; Only RTCC Inturrupt Is used. RTCC Inturrupt is used as timing for Serial Port Receive & Transmit ; Since RS-232 is implemented only as a Half Duplex System, The RTCC is shared by both Receive & ; Transmit Modules. ; Transmission : ; RTCC is setup for Internal Clock increments and interrupt is generated when ; RTCC overflows. Prescaler is assigned, depending on The INPUT CLOCK & the ; desired BAUD RATE. ; Reception : ; When put in receive mode, RTCC is setup for external clock mode (FALLING EDGE) ; and preloaded with 0xFF. When a Falling Edge is detected on RTCC Pin, RTCC ; rolls over and an Interrupt is generated (thus Start Bit Detect). Once the start ; bit is detected, RTCC is changed to INTERNAL CLOCK mode and RTCC is preloaded ; with a certain value for regular timing interrupts to Poll RTCC Pin (i.e RX pin). ; ;********************************************************************************************************* Interrupt: btfss INTCON,T0IF retfie ; other interrupt, simply return & enable GIE ; ; Save Status On INT : WREG & STATUS Regs ; movwf SaveWReg swapf STATUS,W ; affects no STATUS bits : Only way OUT to save STATUS Reg ????? movwf SaveStatus ; btfsc _txmtProgress goto _TxmtNextBit ; Txmt Next Bit btfsc _rcvProgress goto _RcvNextBit ; Receive Next Bit goto _SBitDetected ; Must be start Bit ; RestoreIntStatus: swapf SaveStatus,W movwf STATUS ; restore STATUS Reg swapf SaveWReg, F ; save WREG swapf SaveWReg,W ; restore WREG bcf INTCON,T0IF retfie ; ;********************************************************************************************************* ; ; ; ; Configure TX Pin as output, make sure TX Pin Comes up in high state on Reset ; Configure, RX_Pin (RTCC pin) as Input, which is used to poll data on reception ; ; Program Memory : 9 locations ; Cycles : 10 ;********************************************************************************************************* InitSerialPort: clrf SerialStatus ; bcf STATUS,RP0 ; select Page 0 for Port Access bsf TX ; make sure TX Pin is high on powerup, use RB Port Pullup bsf STATUS,RP0 ; Select Page 1 for TrisB access bcf TX ; set TX Pin As Output Pin, by modifying TRIS if _USE_RTSCTS bcf _RTS ; RTS is output signal, controlled by PIC16Cxx bsf _CTS ; CTS is Input signal, controlled by the host endif bsf RX_Pin ; set RX Pin As Input for reception return ; ;********************************************************************************************************* include "txmtr.asm" ; The Transmit routines are in file "txmtr.asm" include "rcvr.asm" ; The Receiver Routines are in File "rcvr.asm" ;********************************************************************************************************* END