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;*************************************************************************
TITLE "RS232 Communication Using PIC16C54"
;
; Comments :
; (1) Full Duplex
; (2) Tested from 1200 to 9600 Baud( @ 8 Mhz )
; (3) Tested from 1200 to 19200 Baud(@ 16 & 20 Mhz)
;
; The User gets a total time as specified by the User Cycles
; in the table ( or from equations ). The user routine has to
; exactly use up this amount of time. After this time the User
; routine has to give up the control to the Operating System.
; If less than 52 uS is used, then the user should wait in a
; delay loop, until exactly 52 uS.
;
; Transmission :
; Transmit Data is output on DX pin (Bit DX of Port_A).
; In the user routine, the user should load the
; data to be transmitted in the XmtReg and Set the
; X_flag ( bsf FlagRX,X_flag ). This flag gets cleared
; after the transmission.
;
; Reception :
; Data is received on pin DR ( bit DR of Port_A ).
; The User should constantly check the "R_done" flag
; to see if reception is over. If the reception is
; in progress, R_flag is set to 1.
; If the reception is over, "R_done" flag is set to 1.
; The "R_done" flag gets reset to zero when a next start
; bit is detected. So, the user should constantly check
; the R_done flag, and if SET, then the received word
; is in Register "RcvReg". This register gets cleared
; when a new start bit is detected.
;
; Program Memory :
; Total Program Memory Locations Used ( except initialization
; in "main" & User routine ) = 132 locations.
;
; Data Memory :
; Total Data memory locations (file registers used) = 6
; 2 File registers to hold Xmt Data & Rcv Data
; 1 File registers for Xmt/Rcv flag test bits
; 3 File registers for delay count & scratch pad
;
; Stack :
; Only one level of stack is used in the Operating System/RS232
; routine. But this is freed as soon as the program returns to the
; user routine.
;
; RTCC : Not Used
; WDT : Not Used
;
INCLUDE "PICREG.H"
INCLUDE "RS232.H"
;
ORG 0
;*************************************************************************
;
Delay movlw K0+1
movwf DlyCnt ; Total Delay = 3K+6
redo decfsz DlyCnt,Same
goto redo
retlw 0
;
Delay1 movwf DlyCnt
redo_1 decfsz DlyCnt,Same ;
goto redo_1
goto User
;
Delay2 movwf DlyCnt
redo_2 decfsz DlyCnt,Same ; Delay = = 260 Cycles
goto redo_2
goto User_1
;
R_strt btfsc Port_A,DR ; check for a Start Bit
goto ShellY ; delay for 104/2 uS
bcf FlagRX,R_done ; Reset Receive done flag
bsf FlagRX,R_flag ; Set flag for Reception in Progress
btfss FlagRX,BitXsb
bsf FlagRX,A_flag ; A_flag is for start bit detected in R_strt
clrf RcvReg ; Clear all bits of RcvReg
IF R_Nbit
movlw 8 ; 8 Data bits
ELSE
movlw 7 ; 7 data bits
ENDIF
movwf Rcount
goto Shell ; delay for 104+104/4
;
ShellY btfss FlagRX,BitXsb
goto Shell
bsf FlagRX,R_flag
goto Shell
;
R_next bcf STATUS,CARRY
IF R_MODE
rrf RcvReg,Same ; to set if MSB first or LSB first
ELSE
rlf RcvReg,Same
ENDIF
btfsc Port_A,DR
IF R_MODE
IF R_Nbit
bsf RcvReg,MSB ; Conditional Assembly
ELSE
bsf RcvReg,MSB-1
ENDIF
ELSE
bsf RcvReg,LSB
ENDIF
decfsz Rcount,Same
goto Shell
bcf FlagRX,R_flag
bsf FlagRX,S_flag
bsf FlagRX,R_done
goto Shell
;
; Reception Done
;
X_strt bcf Port_A,DX ; Send Start Bit
IF X_Nbit
movlw 8
ELSE
movlw 7
ENDIF
movwf Xcount
IF X_MODE
ELSE
IF X_Nbit
ELSE
rlf XmtReg,Same
ENDIF
ENDIF
goto X_SB
;
X_next bcf STATUS,CARRY
IF X_MODE
rrf XmtReg,Same ; Conditional Assembly
ELSE ; to set if MSB first or LSB first
rlf XmtReg,Same
ENDIF
btfsc STATUS,CARRY
bsf Port_A,DX
btfss STATUS,CARRY
bcf Port_A,DX
decf Xcount,Same
goto X_Data
;
X_SB_1 bcf FlagRX,X_flag ; Xmt flag = 0 -- transmission over
movlw 9
movwf Xcount
bsf Port_A,DX ; Send Stop Bit
goto X_Stop
;
X_SB_2 bsf Port_A,DX
bcf FlagRX,S_bit
goto X_Stop
;
; End of Transmission
;
R0_X0 btfss FlagRX,S_flag
goto User
bcf FlagRX,S_flag
call Delay
movlw K7+1
goto Delay1
;
R1_X0
call Delay
movlw K1+1 ; delay for 1st bit is 104+104/4
movwf DlyCnt
IF R_Nbit
movlw 8 ; 8 Data bits
ELSE
movlw 7 ; 7 data bits
ENDIF
xorwf Rcount,W
btfsc STATUS,Z_bit
goto redo_1
movlw K2+1
goto Delay1
;
R1_X1 ; same as R0_X1
R0_X1 movlw 9
subwf Xcount,W
btfsc STATUS,Z_bit
goto X_strt
movf Xcount,Same ; to check if All data bits Xmted
btfss STATUS,Z_bit
goto X_next
IF SB2
btfsc FlagRX,S_bit
goto X_SB_2
bsf FlagRX,S_bit
goto X_SB_1
ELSE
goto X_SB_1
ENDIF
;
;
X_SB goto cycle4
cycle4 goto X_Data
;
X_Data btfsc FlagRX,A_flag
goto SbDly
btfsc FlagRX,BitXsb
goto ABC
call Delay
movlw K3+1
goto Delay2
;
SbDly bcf FlagRX,A_flag
call Delay
movlw K4+1
goto Delay2
;
ABC bcf FlagRX,BitXsb
call Delay
goto User_1
;
X_Stop
btfsc FlagRX,A_flag
goto SbDly
btfsc FlagRX,BitXsb
goto ABC
call Delay
movlw K5+1
goto Delay2
;
User_1 btfsc FlagRX,R_flag
goto Sync_1 ; Reception already in progress
btfsc FlagRX,S_flag
goto Sync_3
btfsc Port_A,DR ; check for a Start Bit
goto Sync_2 ; No Start Bit - goto User routine
bcf FlagRX,R_done ; Reset Receive done flag
bcf FlagRX,R_flag
bsf FlagRX,BitXsb ; Set flag for Reception in Progress
clrf RcvReg ; Clear all bits of RcvReg
IF R_Nbit
movlw 8 ; 8 Data bits
ELSE
movlw 7 ; 7 data bits
ENDIF
movwf Rcount
goto User
;
Sync_3 bcf FlagRX,S_flag
movlw K6+1
goto Delay1
;
Sync_1
Sync_2 goto User
;
;*************************************************************************
;
Shell btfsc FlagRX,R_flag
goto Chek_X
btfsc FlagRX,X_flag
goto R0_X1
goto R0_X0 ; Case for R0_X0
Chek_X btfsc FlagRX,X_flag
goto R1_X1
goto R1_X0
;
;
;*************************************************************************
; Operating System
; The User routine after time = B/2, should branch Here
;
Op_Sys btfss FlagRX,R_flag
goto R_strt
goto R_next
;
;*************************************************************************
;
main movlw 0EH ; Bit 0 of Port A is Output
tris Port_A ; Set Port_A.0 as output ( DX )
; & Port_A.1 is input ( DR )
bsf Port_A,DX
movlw 9
movwf Xcount ; If Xcount == 9, Then send start bit
clrf FlagRX ; Clear All flag bits.
IF SB2
bsf FlagRX,S_bit ; Set Xmt Stop bit flag(2 Stop Bits)
ELSE
bcf FlagRX,S_bit ; Clear Xmt Stop bit flag
ENDIF
movlw 1FH ; Prescaler = 4
OPTION ; Set RTCC increment on internal Clock
goto Op_Sys
;
;*************************************************************************
;
; ******************* User Routine ***************
; The User routine should use up time exactly = User time as given
; in the Constants Table ( or by Equations for constants ).
; At 9600, this 86 Clock Cycles. RTCC timer is used here to count
; upto 86 cycles ( From 128-86 To 0 ) by examining Bit 7 of RTCC.
;
K_user equ .128+.6-.86
;
User movlw K_user
movwf RTCC
btfsc FlagRX,R_done
goto ErrChk
SetXmt btfsc FlagRX,X_flag
goto Op
movlw 41H
movwf XmtReg
bsf FlagRX,X_flag ; Enable Xmission
goto Op
;
ErrChk
movlw "Z"
xorwf RcvReg,W
btfsc STATUS,Z_bit
goto SetXmt
error goto error ; Received word is not "Z"
;
Op btfss RTCC,MSB ; Test for RTCC bit 7
goto Op ; If Set, Then RTCC has incremented
Oflow goto Op_Sys ; to 128.
;
; ***********************************************************
;
ORG PIC54
goto main
END
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