;
; ***************************************************************************
; ***  Bubble Software Parallax to PIC Source Converter. Copyright 1999.  ***
; ***  http://www.picnpoke.com                 email: sales@picnpoke.com  ***
; ***************************************************************************
;
; SERIN port, pin, baud, polarity, bytes, filter
; Receives data serially at the specified rate and polarity via the specified 
; port pin. Stores the data as a counted string starting at buffer-1 (buffer is 
; the number of bytes in the string). An optional filter causes the routine to
; ignore data outside a range of ASCII character values set by filt_lo and 
; filt_hi. 

	P = pic16c55
	#include <16c55.inc>   ; processor assembler definitions
	_CONFIG _xt_osc & _wdt_off & _protect_off
 reset start

buffer equ d'31' ; String storage. 
B2400 equ d'30' ; Bit delay for 2400 baud. 
B1200 equ d'62' ; Bit delay for 1200 baud. 
B600 equ  d'126'; Bit delay for 600 baud. 
B300 equ  d'255'; Bit delay for 300 baud. 
filt_lo equ  '0'; Set filter for ASCII 
filt_hi equ  '9'; chars representing 0-9. 

 org 8
baud Res d'1' ; Baud rate. 
pin Res d'1' ; Pin number (0-7).
port Res d'1' ; Port number (0-2).
bytes Res d'1' ; Number of bytes to receive. 
temp1 Res d'1' ; Temporary counter for Serin.
temp2 Res d'1' ; Temporary counter for Serin. 
temp3 Res d'1' ; Temporary counter for delay.
ser_fl Res d'1' ; Flags for serin switches. 

polarity equ  ; Polser_fl.0arity: 0=true, 1=inverted. 
filter  equ  ; Ranser_fl.1ge filter: 0=off, 1=on. 
filt_1st equ  ; 1stser_fl.2 filter byte passed?: 0=no, 1=yes. 
aux  equ  ; Temser_fl.3porary flag for filter comparisons. 

; Device data and reset vector
 org 0
; Table to convert pin number (0-7) into bit mask (00000001b to 10000000b). 
Pinz         ADDWF pcl                  
             RETLW d'1'                 
             RETLW d'2'
             RETLW d'4'
             RETLW d'8'
             RETLW d'16'
             RETLW d'32'
             RETLW d'64'
             RETLW d'128'
; Subroutine used by Serin to get a bit and delay for a number of loops
; set by temp3. Jumping into get_bit:loop provides the delay, but ignores the 
; input bit. 
get_bit      MOVF port,w                ; Point to port. 
             MOVWF fsr
             MOVF indirect,w            ; IF Polarity = 0 THEN w = Port 
             BTFSC ser_fl,d'0'          ; ELSE w = NOT Port
             COMF indirect,w            
             ANDWF pin,w                
             BTFSC status,z             ; IF w AND pin THEN carry = 1
             BCF status,c               ; ELSE carry = 0. 
             BTFSS status,z             
             BSF status,c               
             MOVF temp1,w               ; Point to buffer location. 
             MOVWF fsr
             RRF indirect               ; Rotate carry into msb of data byte.
get_bit_loop GOTO $+1                   ; Two-cycle nops. 
             GOTO $+1                   
             GOTO $+1                   
             GOTO $+1                   
             GOTO $+1                   
             DECFSZ temp3               
             GOTO get_bit_loop
             RETLW 0h                   

; Main program start. Receives a single byte of data, filtered for numeric 
; characters, and displays the data bits on LEDs connected to port RB. 
start        MOVLW d'15'                ; All inputs. 
             TRIS 5h
             MOVLW d'0'                 ; All outputs for LEDs.
             TRIS 6h
             CLRF 7h                    ; Clear the LEDs. 
             CLRF ser_fl                ; Clear serial flags.
             MOVLW d'1'                 ; Receive 1 byte 
             MOVWF bytes
             BCF ser_fl,d'1'            ; not filtered 
             BSF ser_fl,d'0'            ; inverted polarity
             MOVLW B2400                ; at 2400 baud 
             MOVWF baud
             MOVLW d'2'                 ; via pin 2 
             MOVWF pin
             MOVLW d'0'                 ; of port ra. 
             MOVWF port
             CALL Serin                 ; Receive the data. 
             MOVF buffer-1,w            ; Move byte to LEDs on RB. 
             MOVWF 6h
             GOTO start                 ; Endless loop

; Body of the Serin routine. Expects the baud constant in baud, number of
; bytes to receive in bytes, the I/O port (0-2 for RA through RC) in port, 
; the pin number (0-7) in pin, and the flag settings in ser_fl 
Serin        CLRF buffer                ; Clear buffer counter. 
             BCF ser_fl,d'2'            
             MOVLW 5h                   ; Add offset for port RA.
             ADDWF port
             MOVF pin,w                 
             CALL Pinz                  ; Get bit mask from the table. 
             MOVWF pin                  ; Put the mask into pin. 
             MOVLW buffer-1             ; Pointer for first data address. 
             MOVWF temp1
Serin_poll   MOVF port,w                
             MOVWF fsr
             MOVF indirect,w            ; IF Polarity = 0 THEN w = Port 
             BTFSC ser_fl,d'0'          ; ELSE w = NOT Port
             COMF indirect,w            
             ANDWF pin,w                ; IF pin = 0 THEN receive data
             BTFSS status,z             ; ELSE poll
             GOTO Serin_poll
             BCF status,c               
             RRF baud,w                 ; LET temp3 = baud/2
             MOVWF temp3                ; Set up 1/2 bit time delay. 
             CALL get_bit_loop          ; Jump into delay of get_bit.
             MOVF baud,w                ; Set up full bit time delay. 
             MOVWF temp3
             CALL get_bit_loop          ; Jump into delay of get_bit.
             MOVLW d'8'                 ; Eight data bits.      
             MOVWF temp2
Serin_rcv    MOVF baud,w                ; Set up bit delay.
             MOVWF temp3
             CALL get_bit               ; Get the next data bit.
             DECFSZ temp2               ; Eight bits received?
             GOTO Serin_rcv
Serin_done   MOVF baud,w                ; Set up bit delay.
             MOVWF temp3
             CALL get_bit_loop          ; Wait for stop bit.
             BTFSS ser_fl,d'1'          ; IF filter=0 (off) THEN :skip
             GOTO Serin_skip
             BCF ser_fl,d'3'            ; LET aux = 0. 
             MOVLW filt_lo              ; IF byte < filt_lo THEN aux=1
             SUBWF indirect,w
             BTFSS status,c
             BSF ser_fl,d'3'            
             MOVLW ~filt_hi             ; IF byte > filt_hi THEN aux=1
             ADDWF indirect,w
             BTFSC status,c
             BSF ser_fl,d'3'            
             BTFSS ser_fl,d'3'          ; If aux = 0 (byte is within 
             GOTO Serin_skip
             BTFSC ser_fl,d'2'          ; filter range) :skip. If byte is
             RETLW 0h                   ; out of range, but valid bytes have 
             GOTO Serin_poll            ; been received, return. Else poll. 
Serin_skip   BSF ser_fl,d'2'            
             DECF temp1                 ; Decrement buffer pointer. 
             INCF buffer                ; Increment buffer counter. 
             DECFSZ bytes               ; More bytes to receive: poll.
             GOTO Serin_poll
             RETLW 0h                   

             
             
             end