;*************************************************************************** ;*************************************************************************** ; ****** THE FOLLOWING ARE SUB-ROUTINES ******* ; ****** CALLED BY THE MAIN PROGRAM ******* ;*************************************************************************** ;*************************************************************************** ;*** SWITCH PRESCALER BETWEEN WDT AND RTCC *** (PrScale, NoPrScl) *** ;*** THIS PROCEDURE, DOCUMENTED IN SPEC. SHEET SECTION 9.1, IS INTENDED TO ;*** PREVENT UNEXPECTED RESET CONDITION ;*** PrScale ROUTINE CALLED AT END OF AttnSig AND Srq SIGNALS PrScale clrwdt ; Change prescaler from WDT to RTCC movlw b'00000001' ; BINARY - set to prescale RTCC option ; Clear 4th bit from right to select RTCC clrf TMR0 ; last 3 bits set prescale value as 1:4 retlw NULL ; this gives a good ratio to monitor the ; timing for Reset and Attention signals and ; the 2nd Application Task ;*** NoPrScl ROUTINE CALLED AT BEGINNING OF SyncSig AND END OF Srq SIGNALS NoPrScl clrf TMR0 ; Change prescaler from RTCC to WDT movlw b'00001000' ; Set 4th bit from right to select WDT option clrwdt movlw b'00001000' option retlw NULL ;*************************************************************************** ;*** GET INCOMING BIT & INTERPRET WHETHER IT'S A '1' OR A '0' *** (Get_Bit) *** ;*** Get_Bit CALLED BY COMMAND AND LISTEN ROUTINES ; Get the bit, find out whether it's less than or greater than 50 usecs, ; if < than 50 usecs, it's a '1' bit ; if > than 50 usecs, it's a '0' bit ; if it's a '1' bit, set LSB in the reg. pointed to by the FSR (Command Byte) ; if it's a '0' bit, do nothing to the LSB ; then look for the end of the Bit Cell (104 usecs max.) ; if the maximum Bit time of (72 usecs) or maximum Bit Cell time is exceeded, ; abort to the Attn Signal Get_Bit movf TMR0,W ; Check the time, then check if the line went high: subwf TimeVar,W ; See if more than BIT_TST usecs have passed btfss STATUS,C; if not, check whether the line went high goto AttnSig ; if so, abort to the Attn Signal btfss PORTA,ADB ; Check whether the line went high goto Get_Bit ; if line is still low, loop again movlw BIT_TST ; if line went high, see if it's a '1' or a '0' movwf TimeVar ; as the bit has not yet been determined yet, bcf INDF,LSB ; ensure the LSB in the indirect address is '0' movf TMR0,W ; Get the time subwf TimeVar,W ; if time < 50 usecs, it's a '1' bit btfsc STATUS,C; if time > 50 usecs and < 72, it's a '0' bit bsf INDF,LSB ; if it's a 1, set LSB in the address FSR points to movlw BITCELL ; Check whether the Max. Bit Cell time of 104 usecs movwf TimeVar ; has been exceeded CellChk movf TMR0,W ; Check the time, then check the line subwf TimeVar,W ; See if more than Max. Bit Cell usecs have passed btfss STATUS,C; if not, look for the line to go low again goto AttnSig ; if so, abort to the Attn Signal or Reset btfsc PORTA,ADB ; Check the line for the start of another bit goto CellChk ; if the line is still high, loop CelChk1 again clrf TMR0 ; if the line went low, clear the RTCC & return retlw NULL ; for another bit or to interpret the Command ;*************************************************************************** ;*** DETERMINE IF THIS IS A GLOBAL COMMAND TO ALL DEVICES *** (Globals) *** ;*** Globals CALLED BY AddrChK Globals movf TmpReg2,W ; Check whether the Command is for all devices xorlw C_RES_1 ; retrieve the Command Type (the upper 2 bits of btfsc STATUS,Z ; the Command nibble) goto Reserv1 ; test for this being the first Reserved Command movf TmpReg1,W ; retrieve the whole Command Nibble xorlw C_RES_2 ; test for this being the second Reserved Command btfsc STATUS,Z goto Reserv2 movf TmpReg1,W ; retrieve the whole Command Nibble xorlw C_RES_3 ; test for this being the third Reserved Command btfsc STATUS,Z goto Reserv3 xorlw C_RESET ; test for this being Reset Command btfsc STATUS,Z goto Reset retlw NULL ;*************************************************************************** ;*** MASK OUT COMMAND NIBBLE AND REG.# BITS FROM THE COMMAND *** (MaskCmd) *** ; NOTE: This routine should only be called once during any single ADB ; transaction, from either AddrChk or CmmdChk MaskCmd movf CmdByte,W ; Mask the Command to save the Data Reg. # bits & andlw CMDNIBL ; the Command Type bits (Listen, Talk, etc.): movwf TmpReg1 ; save the Command nibble andlw CMDTYPE ; mask the upper 2 Command Type bits (Talk, etc.) movwf TmpReg2 ; save the upper 2 Command Type bits movf CmdByte,W ; extract the Data Register number: andlw REGMASK ; mask out Data Reg. number from Command Nibble movwf RegNum ; save the Data Reg. bits movwf FSR ; save pointer to Data Reg. in File Select Reg. ; in order to setup RAM address where start ; of Data for this Reg. will be stored SaveRAM bcf STATUS,C; clear Carry bit so it doesn't wrap around rlf FSR,F ; multiply by 2 to get 1st Byte of RAM addr bsf FSR,03h ; add array offset for Send/Receive/Flush Reg. movf FSR,W ; by setting bit of 1st RAM address, which andlw FSRMASK ; is ORG'd in ADB.EQU equates movwf RAMaddr ; mask out the RAM address of Data Reg. Number retlw NULL ; save RAM address of Data Reg. and return ;*************************************************************************** ;*** ISSUE A SERVICE REQUEST IF NECESSARY *** (Srq; may call LineLow) *** ;*** CALLED BY AddrChk ; see if the Srq Flag is set, if not, return, otherwise: ; change the prescaler to RTCC since this takes longer than 255 usecs, ; load the SRQTIME of 300 usecs into the TimeVariable, ; call LineLow to: ; keep checking the time to see if 300 usecs have passed, ; let the line go high again, ; and see if the line is high, and if not, abort, if it is, ; change the prescaler back to WDT, and return Srq btfss Flags2,F2Srq; see if the Srq flag is set, retlw NULL ; if not, return call PrScale ; switch the prscaler to RTCC movlw TRI_OUT ; tri-state PORTA to make the ADB an output tris PORTA movlw SRQ_MAX call LineLow call NoPrScl ; change the prescaler back to WDT retlw NULL ;*************************************************************************** ;*** Tlt - TIME FROM STOP BIT TO START BIT *** (Tlt) *** ;*** CALLED BY EITHER Talk OR Listen ROUTINES ; Loop checking the time, then checking the line to see if it went low ; if at any time the line goes low, ; see if this is a Talk Command, ; if it is a Talk Commmand, go to the Collision routine ; if the line goes low before the minimum Tlt time, abort to Attn Signal ; if the line is high longer than TLT_Min usecs, ; see if this is a Talk Command, and if it is, wait for the mid-point, ; and return to Send the Start Bit, Data Bytes, & the Stop Bit ; if it's not a Talk Command, see if it's a Listen Command, and if so, ; load Tlt_Max for TimeVariable, and look for the line to go ; low as the beginning of the Start Bit, ; if more than Tlt_Max usecs pass, abort to Attn Signal ; if the line goes low and this is a Listen Command, ; clear the RTCC & return to get the rest of the Start Bit Tlt movlw TLT_MIN ; Look for Stop-to-Start-Time, Tlt movwf TimeVar ; Check the time, then check the line TltChk1 movf TMR0,W ; See if more than TLT_MIN usecs have passed xorwf Random,F ; (ensure the Talk R3 address is Random with XOR) subwf TimeVar,W ; by checking whether Carry bit is set btfss STATUS,C; after subtraction goto ChkFlag ; if TLT_MIN usecs passed, see what Command this is btfsc PORTA,ADB ; if not, check whether the line went low goto TltChk1 ; if the line is still high, keep looping btfsc Flags1,F1Talk; if line went low, see if this is a Talk Command goto Collisn ; if it is, there was a Collision, abort movf TMR0,W ; otherwise, check the time subwf TimeVar,W ; see if TLT_MIN usecs passed, btfss STATUS,C; if not, abort to Attn Signal, too little goto AttnSig ; time passed when the line went low clrf TMR0 ; if it's not a Talk Command, clear the RTCC and retlw NULL ; return for the rest of the Start Bit ChkFlag btfsc Flags1,F1Talk; Check whether to Talk or Listen goto TltTalk ; if Talk, wait for mid-point of Tlt time btfss Flags1,F1Lstn; if Listen, continue to look for Start Bit retlw NULL ; if neither flag is set, abort, something's wrong movlw TLT_MAX ; Load TimeVariable to check for upper limit movwf TimeVar ; of Tlt time TltChk2 movf TMR0,W ; See if TLT_MAX usecs have been exceeded subwf TimeVar,W ; by checking whether Carry bit is set btfss STATUS,C; after subtraction goto AttnSig ; if so, abort to Attn Signal btfsc PORTA,ADB ; if not, check whether the line went low goto TltChk2 ; if line is still high, check the time again btfsc Flags1,F1Talk; if line went low, see if this is a Talk Command goto Collisn ; if so, there was a Collision clrf TMR0 ; if it's not a Talk Command, return to get retlw NULL ; the rest of the Start Bit from Host TltTalk movlw TLT_MID ; Load TimeVariable so Talk will send Start Bit at movwf TimeVar ; about the mid-point of the Tlt TltChk3 movf TMR0,W ; See if TLT_MID usecs have been exceeded subwf TimeVar,W ; by checking whether Carry bit is set btfss STATUS,C; after subtraction retlw NULL ; if time was exceeded, return to send Start Bit btfsc PORTA,ADB ; if not, check whether the line went low goto TltChk3 ; if line is still high, check the time again goto Collisn ; if the line went low, abort to Collision ;*************************************************************************** ;*** MAKE LINE GO LOW TIME IN TimeVar AS A '1' OR '0' BIT *** (LineLow) *** ;*** CALLED BY Talk OR Srq LineLow movwf TimeVar ; Low_Tmp movf TMR0,W ; Check the clock, subwf TimeVar,W ; loop until TimeVar usecs have passed btfsc STATUS,C; goto Low_Tmp ; movlw TRI_IN ; Tri-state PORTA to make ADB line an input again tris PORTA ; and let the line go high clrf TMR0 ; and clear RTCC nop ; Allow the ADB Port line to stabilize nop ; Allow the ADB Port line to stabilize btfss PORTA,ADB ; check if the line is still low, if so, a goto Collisn ; Collision occurred retlw NULL ; if not, return to load high time for rest of bit ;*** MAKE LINE GO HIGH FOR REST OF BIT CELL TIME IN TimeVar *** (LineHi) *** ;*** CALLED BY Talk LineHi movwf TimeVar ; Let the line go high for a pre-designated time Hi_Tmp movf TMR0,W ; Check the clock, subwf TimeVar,W ; loop until TimeVar usecs have passed btfsc STATUS,C; goto Hi_Tmp ; btfss PORTA,ADB ; check if the line is still high, goto Collisn ; if not, a Collision occurred, Abort btfsc Flags1,F1Stop; if this is the end of the Data Stop Bit, don't retlw NULL ; let the line go low again, just return movlw TRI_OUT ; if still high, start sending a bit to the Host tris PORTA ; tri-state PORTA to make the ADB an output and clrf TMR0 ; return retlw NULL ; ;*************************************************************************** ;*************************************************************************** ; ****** END OF SUB-ROUTINES ******* ;*************************************************************************** ;***************************************************************************