Hello every one,
After searching here and on net when I did not find the information I needed I thought lets put everything that I have done so that some one can provide helpful reply.
I have made a working intercom unit using AT89c52 and with following hardware details, the system is working perfectly with one digit dialing.
I code which is pasted below is for four lines mini-exchange and is helpful i guess for any one trying to make a microcontroller based intercom as i found that there is no specific code available here about an intercom exchange.
Now I want to use CLI device with each set in such a way that each CLI device, what improvement or addition the code should have in order to send data to the CLI device in such a way that no hardware addition is done as CLI (encoder or decorder nothing), is it possible to use the coding only to send data to a CLI device in my case.

Its just a four line intercom unit which is only for pulse dialing telephone sets (its does not mean that its a PBX telephone set act as intercoms) means no Tone Dialing encoding IC is used, controller is used to decode the dialed number from the set since it is pulse dialing.

Numbering of the set is : 1 , 2 , 3 , 4

Objective is each telephone set has a CLI device contacted in a normal way now when telephone 1 calls telephone 2 , the CLI attach with telephone 2 shows the calling party's number to the receiving party means telephone 2 user knows that telephone 1 is calling him. Now how what changes should be done in the code in order to get CLI working for this mini-exchange.

Hardware Details

Crystal :- 11.052 MHz

Controller:- AT89c52

Analog Switch: MT8816

Port 2 :- Controller receives High signal for Off Hook , Low for On Hook & Pulse Dialing signals. (So I don’t send P2 00000000 in the start of the code becuase as the power goes on P2 automatically becomes low due to hardware arrangement, now please don’t say that it has be the other way around because hardware is fine and working perfectly only code improvement is needed)

Port 1:- Controller sends 8 bit data to MT8816.

Port 3:- P 3.7 strobe of MT8816

CS pin of MT8816 is already set high through hardware arrangement so no need to think about any other pin of MT8816 in order to make or break connection of rows and columns.

Port 0: Controller sends ringing signals to the 5 volts relays when ever ringing is required on any set.

CODE for FOUR Lines Intercom considering the above arrangement:

;Macro definition of timer0 in 16 bit itmer mode

;***********************************MACRO DEFINITION FOR PRODUCING REQUIRED DELAYS*************************************
;The follwing macro implements the logic to produce any amount of required delays in the program. The required delay is
;passed as an argument in the form of a hexadecimal number, which is used as a preset value of timer0 to make the timer
;overflow after a certain interval of time.
;**********************************************************************************************************************

TIMER00 MACRO HIGHVALUE0, LOWVALUE0
LOCAL WAIT

CLR TF0 ;clear overflow flag
CLR TR0 ;stop timer
MOV TH0,#HIGHVALUE0 ;load high value
MOV TL0,#LOWVALUE0 ;load low value
SETB TR0 ;start timer
WAIT: JNB TF0,WAIT ;check overflow flag
CLR TF0 ;clear overflow flag
CLR TR0 ;stop timer
ENDM ;end of macro


;*******************************************MACRO DEFINITIONS FOR EACH SET********************************************

;*******************************************MACRO FOR SET1************************************************************
;Macro definition for specific operations for each number
;The code is written for Set '1' and this set can call the sets 2,3,4

CON_DIALNUMBER01 MACRO RING_BIT, LABEL_RESTART, DIAL_VALUE,DIAL_BIT, DIAL_VALUE_REM, CON_FLAG
LOCAL REPEAT, CONNECT, REMCONNECT, CHECK, AGAIN, AGAIN2, DUMMY,STILLCONNECT

JB DIAL_BIT,DUMMY ;send P2.n, which is already offhook
JB CON_FLAG,DUMMY ;if this set is already receiving ringing from another set
REPEAT: SETB RING_BIT ;sendringing signal to dialed number
SETB CON_FLAG ;ensure that the dialed set is in continuing to connect...
MOV P1,#090H ;send dial tone form P2.0
MOV R1,#010H ;laod '10' in r1 for continuous loop

AGAIN: TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)

DJNZ R1, AGAIN ;decrement and jump if not 0
CPL RING_BIT ;compliment in order to send ringing signal
MOV P1,#010H ;send for ringback tone(connect X2,Y0)
MOV R1,#010H ;in order to create half second delay

AGAIN2: TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)

DJNZ R1, AGAIN2 ;decrement and jump if not zero
INC R2 ;increment counter of ringing signal
JB DIAL_BIT, CONNECT ;picked up before 8rings
JNB P2.0,REMCONNECT ;if dialed set goes to onhook
CJNE R2,#008H,REPEAT ;ring continous til 8rings
CLR RING_BIT ;remove ringing signal if not picked up before 8 rings
CLR CON_FLAG ;ensure that the dialed set is now NOT connected
MOV P1,#010H ;remove ring back tone
DUMMY: JMP INCORRECT01 ;proceed as incorrect number
CONNECT: CLR RING_BIT ;remove ringing signal
SETB CON_FLAG ;ensure that the dialed set is already connected
MOV P1,#010H ;remove ring back tone
MOV P1,#097H ;connect X2 with y7
MOV P1, #DIAL_VALUE ;connect dial set with y7
JNB P2.0, CHECK ;if set1 goes on hook
;JNB DIAL_BIT, CHECK ;if dialed set goes on hook
;LJMP CONNECT ;else continuous connectionis made
STILLCONNECT: JB P2.0,$ ;still connection until set1 goes onhook

CHECK: TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)

JNB P2.0, REMCONNECT ;if still on hook i.e. valid on hook
;JNB DIAL_BIT, REMCONNECT ;if still on hook i.e.valid on hook
LJMP STILLCONNECT ;else invalid on hook
REMCONNECT: MOV P1,#017H ;remove connection X2,Y7
CLR CON_FLAG ;ensure that the dialed set is now NOT connected
MOV P1,#DIAL_VALUE_REM ;remove connection dialed set
MOV R0,#000H ;reinitializethe pulse counter
MOV R2,#000H ;reinitializethe ringing counter
LJMP WAITOFFHOOK01 ;go back, restart theprogram
ENDM ;END OF MACRO


;*********************************MACRO FOR SET2****************************************

CON_DIALNUMBER02 MACRO RING_BIT, LABEL_RESTART, DIAL_VALUE,DIAL_BIT, DIAL_VALUE_REM, CON_FLAG
LOCAL REPEAT, CONNECT, REMCONNECT, CHECK, AGAIN, AGAIN2,DUMMY,STILLCONNECT

JB DIAL_BIT, DUMMY ;send P2.n, which is already offhook
JB CON_FLAG,DUMMY ;if this set is already receiving ringing from anotherset
REPEAT: SETB RING_BIT ;sendringing signal to dialed number
SETB CON_FLAG ;ensure that the dialed set is in continuing to connect...
MOV P1,#098H ;send dial tone form P2.1
MOV R1,#010H ;laod '10' in r1 for continuous loop

AGAIN: TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)

DJNZ R1, AGAIN ;decrement and jump if not 0
CPL RING_BIT ;compliment in order to send ringing signal
MOV P1,#018H ;send for ringback tone
MOV R1,#010H ;in order to create half second delay

AGAIN2: TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)

DJNZ R1, AGAIN2 ;decrement and jump if not zero
INC R2 ;countringing signal
JB DIAL_BIT, CONNECT ;picked up before 8rings
JNB P2.1,REMCONNECT ;if dialed set goes to onhook
CJNE R2,#008H,REPEAT ;ring continous til 8rings
CLR RING_BIT ;remove ringing signal if not picked up before 8 rings
CLR CON_FLAG ;ensure that the dialed set in now NOT connected to any set
MOV P1,#018H ;remove ring back tone
DUMMY: LJMP INCORRECT02 ;proceed as incorrect number
CONNECT: CLR RING_BIT ;remove ringing signal
SETB CON_FLAG ;ensure that the dialed set is already connected
MOV P1,#018H ;remove ring back tone
MOV P1,#09EH ;connect X3 with y6
MOV P1, #DIAL_VALUE ;connect dial set with y6
;JNB P2.1, CHECK ;if set1 goes on hook
;JNB DIAL_BIT, CHECK ;if dialed set goes on hook
;LJMP CONNECT ;else continuous connectionis made
STILLCONNECT:JB P2.1,$ ;still connection until set2 goes onhook

CHECK: IMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)

JNB P2.1, REMCONNECT ;if still on hook i.e. valid on hook
;JNB DIAL_BIT, REMCONNECT ;if still on hook i.e.valid on hook
LJMP STILLCONNECT ;else invalid on hook
REMCONNECT: MOV P1,#01EH ;remove connection X3,Y6
CLR CON_FLAG ;ensure that the dialed set is now NOT connected
MOV P1,#DIAL_VALUE_REM ;remove connection dialed set
MOV R0,#000H ;reinitializethe pulse counter
MOV R2,#000H ;reinitializethe ringing counter
LJMP WAITOFFHOOK02 ;go back, restart theprogram
ENDM ;END OF MACRO

;*********************************MACRO FOR SET3****************************************

CON_DIALNUMBER03 MACRO RING_BIT, LABEL_RESTART, DIAL_VALUE,DIAL_BIT, DIAL_VALUE_REM, CON_FLAG
LOCAL REPEAT, CONNECT, REMCONNECT, CHECK, AGAIN, AGAIN2,DUMMY,STILLCONNECT

JB DIAL_BIT, DUMMY ;send P2.n, which is already offhook
JB CON_FLAG,DUMMY ;if this set is already receiving ringing from another set
REPEAT: SETB RING_BIT ;sendringing signal to dialed number
SETB CON_FLAG ;ensure that the dialed set is in continuing to connect...
MOV P1,#0A0H ;send dial tone form P2.2
MOV R1,#010H ;laod '10' in r1 for continuous loop

AGAIN: TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)

DJNZ R1, AGAIN ;decrement and jump if not 0
CPL RING_BIT ;compliment in order to send ringing signal
MOV P1,#020H ;send for ringback tone
MOV R1,#010H ;in order to create half second delay

AGAIN2: TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)

DJNZ R1, AGAIN2 ;decrement and jump if not zero
INC R2 ;countringing signal
JB DIAL_BIT, CONNECT ;picked up before 8rings
JNB P2.2,REMCONNECT ;if dialed set goes to onhook
CJNE R2,#008H,REPEAT ;ring continous til 8rings
CLR RING_BIT ;remove ringing signal if not picked up before 8 rings
CLR CON_FLAG ;ensure that the dialed set in now NOT connected to any set
MOV P1,#020H ;remove ring back tone
DUMMY: LJMP INCORRECT03 ;proceed as incorrect number
CONNECT: CLR RING_BIT ;remove ringing signal
SETB CON_FLAG ;esure that the dialed set is already connected
MOV P1,#020H ;remove ring back tone
MOV P1,#0A5H ;connect X4 with y5
MOV P1, #DIAL_VALUE ;connect dial set with y5
;JNB P2.1, CHECK ;if set1 goes on hook
;JNB DIAL_BIT, CHECK ;if dialed set goes on hook
;LJMP CONNECT ;else continuous connectionis made

STILLCONNECT:JB P2.2,$ ;sill connection until set3 goes onhook

CHECK: TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)

JNB P2.2, REMCONNECT ;if still on hook i.e. valid on hook
;JNB DIAL_BIT, REMCONNECT ;if still on hook i.e.valid on hook
LJMP STILLCONNECT ;else invalid on hook
REMCONNECT:MOV P1,#025H ;remove connection X4,Y5
CLR CON_FLAG ;ensure that the dialed set is now NOT connected
MOV P1,#DIAL_VALUE_REM ;remove connection dialed set
MOV R0,#000H ;reinitializethe pulse counter
MOV R2,#000H ;reinitialize the ringing counter
LJMP WAITOFFHOOK03 ;go back, restart theprogram
ENDM ;END OF MACRO

;*********************************MACRO FOR SET4****************************************

CON_DIALNUMBER04 MACRO RING_BIT, LABEL_RESTART, DIAL_VALUE,DIAL_BIT, DIAL_VALUE_REM, CON_FLAG
LOCAL REPEAT, CONNECT, REMCONNECT, CHECK, AGAIN, AGAIN2,DUMMY,STILLCONNECT

JB DIAL_BIT, DUMMY ;send P2.n, which is already offhook
JB CON_FLAG,DUMMY ;if this set is already receiving ringing from another set
REPEAT: SETB RING_BIT ;sendringing signal to dialed number
SETB CON_FLAG ;ensure that the dialed set is in continuing to connect...
MOV P1,#0A8H ;send dial tone form P2.3
MOV R1,#010H ;laod '10' in r1 for continuous loop
AGAIN: TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)
DJNZ R1, AGAIN ;decrement and jump if not 0
CPL RING_BIT ;compliment in order to send ringing signal
MOV P1,#028H ;send for ringback tone
MOV R1,#010H ;in order to create half second delay
AGAIN2: TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)
DJNZ R1, AGAIN2 ;decrement and jump if not zero
INC R2 ;countringing signal
JB DIAL_BIT, CONNECT ;picked up before 8rings
JNB P2.3,REMCONNECT ;if dialed set goes to onhook
CJNE R2,#008H,REPEAT ;ring continous til 8rings
CLR RING_BIT ;remove ringing signal if not picked up before 8 rings
CLR CON_FLAG ;ensure that the dialed set in now NOT connected to any set
MOV P1,#028H ;remove ring back tone
DUMMY: LJMP INCORRECT04 ;proceed as incorrect number

CONNECT: CLR RING_BIT ;remove ringing signal
SETB CON_FLAG ;ensure that the dialed set is already connected
MOV P1,#028H ;remove ring back tone
MOV P1,#0ACH ;connect X5 with y4
MOV P1, #DIAL_VALUE ;connect dial set with y4
;JNB P2.1, CHECK ;if set1 goes on hook
;JNB DIAL_BIT, CHECK ;if dialed set goes on hook
;LJMP CONNECT ;else continuous connectionis made
STILLCONNECT:JB P2.3,$ ;still connection until set3 goes onhook

CHECK: TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)

JNB P2.3, REMCONNECT ;if still on hook i.e. valid on hook
;JNB DIAL_BIT, REMCONNECT ;if still on hook i.e.valid on hook
LJMP STILLCONNECT ;else invalid on hook
REMCONNECT:MOV P1,#02CH ;remove connection X5,Y4
CLR CON_FLAG ;ensure that the dialed set is now NOT connected
MOV P1,#DIAL_VALUE_REM ;remove connection dialed set
MOV R0,#000H ;reinitializethe pulse counter
MOV R2,#000H ;reinitialize the ringing counter
LJMP WAITOFFHOOK04 ;go back, restart theprogram
ENDM ;END OF MACRO

;***********************************Start of Code*********************************************
ORG 0000H ;reset
LJMP MAIN ;jump to main program
ORG 0001BH ;Vector address of timer1
LJMP T1ISR ;jump to scheduler ISR
ORG 0030H ;start of program
CONST EQU 200D
CONST2 EQU 100D
DELAY_50ms EQU 0CF2CH ;12.5ms+((2.5*15021)/1000)=50ms
DELAY_25ms EQU 0E69CH ;6.5+((1.3*15021)/1000)=25ms


;***********************************MAIN PROGRAM******************************

MAIN: MOV P0,#000H ;sothat at start the phones are not ringing
MOV P1,#000H ;reset MT8816address and data pin
MOV P3,#000H ;reset port3
MOV B,#000H ;reset connection flags
MOV TMOD,#011H ;use timer0 and timer1 in mode 1(16 bit timer mode)
MOV TH1,#0ECH ;load high byte values of timer1
MOV TL1,#078H ;load low byte value of timer1
SET1 EQU 030H ;starting address of code for set1
SET2 EQU 03CH ;starting address of code for set2
SET3 EQU 048H ;starting address of code for set3
SET4 EQU 054H ;starting address of code for set1
SETB EA ;enavle global interrupt
SETB ET1 ;enable timer1 interrupt
SETB RS1 ;set register bank select bit1
SETB RS0 ;set register bank select bit2
MOV R0, #SET1 ;have to start execution from set1
CLR RS1 ;clear register bank select bit0
CLR RS0 ;clear register bank select bit1
MOV R0,#000H ;used for pulsecounter
MOV R2,#000H ;to count ringing signal
SETB P3.7 ;set strobe pin
MOV 031H, #HIGH(WAITOFFHOOK01) ;save high byte of address of set1 code
MOV 032H , #LOW(WAITOFFHOOK01) ;save low byte of address of set1 code
MOV 03DH, #HIGH(WAITOFFHOOK02) ;save high byte of address of set2 code
MOV 03EH, #LOW(WAITOFFHOOK02) ;save low byte of address of set2 code
MOV 049H ,#HIGH(WAITOFFHOOK03) ;save high byte of address of set3 code
MOV 04AH ,#LOW(WAITOFFHOOK03) ;save low byte of address of set3 code
MOV 055H ,#HIGH(WAITOFFHOOK04) ;save high byte of address of set4 code
MOV 056H ,#LOW(WAITOFFHOOK04) ;save lowbyte of address of set4 code
MOV 03FH,#00H ;clear connection flag space
SETB TR1 ;start timer1 (use for scheduling)

;*******************************SET1 CODE***************************************

WAITOFFHOOK01: JNB P2.0,$ ;check continuously whether the set is offhook
JB B.0,WAITOFFHOOK01 ;if already connected
MOV P1,#090H
MOV R1,#CONST ;initialize 5 sec counter
AGAIN01: TIMER00 HIGH(DELAY_25ms),LOW(DELAY_25ms) ;call macro with high and low value of (-25000)

JNB P2.0,PULSEDIALED01 ;if pulse dialed?
DJNZ R1,AGAIN01 ;decrement and jump if no t zero
MOV P1,#10H ;remove dial tone if no activity for 5 sec
LJMP WAITONHOOK01 ;wait for offhook again

PULSEDIALED01: MOV P1,#010H ;remove dialtone

LOW_PUSLEWIDTH_COUNTER01: MOV R1,#CONST ;200*250 usec=50 ms

AGAIN201: TIMER00 0FFH,006H ;call macro with high and low value of (-250)

JB P2.0,HIGH_PULSEWIDTH_COUNTER01 ;jump if valid pulse

DJNZ R1,AGAIN201 ;decrement and jump if not zero
MOV P1,#010H ;remove dial tone,not valid pulse, set is on hook
LJMP WAITOFFHOOK01 ;again check and wait for offhook

HIGH_PULSEWIDTH_COUNTER01: INC R0 ;count pulses
MOV R1,#CONST ;200*325usec= 65 msec
AGAIN301: TIMER00 0FEH,0BBH ;call macro with (-325)

JNB P2.0, LOW_PUSLEWIDTH_COUNTER01 ;pulse again

DJNZ R1,AGAIN301 ;decrement and jump if not zero

;DIALED NUMBER IS LOADED IN R0.NOW CHECK FOR VALID NUMBER

MOV DPTR,#0D00H ;laod base register in DPTR
MOV A,R0 ;laod dialed number in accumulator as offset
MOVC A,@A+DPTR ;laod the dialed number from lookup table by offset
CLR C ;in order to perfomr subtractionsuccesfully
SUBB A,R0 ;(A)<---- (A)-(R0)to check whether the dialed number is valid
CJNE A,#000H,INCORRECT01 ;incorrect number
CJNE R0,#001H,CORRECT01 ;else dialed the same set number
LJMP NUMBER101 ;number 1 is dialed


CORRECT01: CJNE R0,#002H,NEXT01 ;if dialed number is not 2
LJMP NUMBER201 ;if dialed number is 2
NEXT01: CJNE R0,#003H,NEXT201 ;not 3
LJMP NUMBER301 ;if dialed number is 3
NEXT201: LJMP NUMBER401 ;Therefore ultimate dialed number is 4
INCORRECT01: MOV P1,#090H ;dial tone
MOV R1,#010H

AGAIN4401: TIMER00 HIGH(DELAY_25ms),LOW(DELAY_25ms) ;call macro with high and low value of (-25000)

JNB P2.0,RESTART01 ;if set onhook
DJNZ R1,AGAIN4401 ;decrement and jump if not zero
MOV P1,#010H ;set dial tone to generate engage tone
MOV R1,#010H
AGAIN5501: TIMER00 HIGH(DELAY_25ms),LOW(DELAY_25ms) ;call macro with high and low value of (-25000)
JNB P2.0 ,RESTART01 ;if onhook
DJNZ R1,AGAIN5501 ;decrement and jump if not zero
LJMP INCORRECT01 ;else onhook

RESTART01: MOV P1,#010H ;remove engage tone
MOV R0,#000H ;reinitialize the pulse counter
LJMP WAITONHOOK01 ;resatart theprogram
NUMBER101: MOV R0,#000H ;reinitializepulse counter
MOV P1,#010H
LJMP INCORRECT01

NUMBER201: CON_DIALNUMBER01 P0.1, RESTART01, 09FH, P2.1, 01FH, B.1
NUMBER301: CON_DIALNUMBER01 P0.2, RESTART01, 0A7H, P2.2, 027H, B.2
NUMBER401: CON_DIALNUMBER01 P0.3, RESTART01, 0AFH, P2.3, 02FH, B.3


WAITONHOOK01: JB P2.0,WAITONHOOK01 ;wait for onhook

TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)
JB P2.0,WAITONHOOK01 ;not valid onhook
LJMP WAITOFFHOOK01 ;valid offhook! restart...


;*******************************SET2 CODE***************************************

WAITOFFHOOK02:JNB P2.1,$ ;check continuously whether the set is offhook
JB B.1,WAITOFFHOOK02 ;if already connected
MOV P1,#098H ;send dialtone
MOV R1,#CONST ;initialize 5 sec counter
AGAIN02: TIMER00 HIGH(DELAY_25ms),LOW(DELAY_25ms) ;call macro with high and low value of (-25000)

JNB P2.1,PULSEDIALED02 ;if pulse dialed?
DJNZ R1,AGAIN02 ;decrement and jump if no t zero
MOV P1,#018H ;remove dial tone if no activity for 5 sec
LJMP WAITONHOOK02 ;wait for offhook again
PULSEDIALED02:MOV P1,#018H ;remove dialtone

LOW_PUSLEWIDTH_COUNTER02: MOV R1,#CONST ;200*250 usec=50 ms

AGAIN202: TIMER00 0FFH,006H ;call macro with high and low value of (-250)

JB P2.1,HIGH_PULSEWIDTH_COUNTER02 ;jump if valid pulse

DJNZ R1,AGAIN202 ;decrement and jump if not zero
MOV P1,#018H ;remove dial tone,not valid pulse, set is on hook
LJMP WAITOFFHOOK02 ;again check and wait for offhook

HIGH_PULSEWIDTH_COUNTER02: INC R0 ;count pulses
MOV R1,#CONST ;200*325usec= 65 msec
AGAIN302: TIMER00 0FEH,0BBH ;call macro with (-325)
JNB P2.1, LOW_PUSLEWIDTH_COUNTER02 ;pulse again
DJNZ R1,AGAIN302 ;decrement and jump if not zero

;DIALED NUMBER IS LOADED IN R0.NOW CHECK FOR VALID NUMBER

MOV DPTR,#0D00H ;laod base register in DPTR
MOV A,R0 ;laod dialed number in accumulator as offset
MOVC A,@A+DPTR ;laod the dialed number from lookup table by offset
CLR C ;in order to perfomr subtractionsuccesfully
SUBB A,R0 ;(A)<---- (A)-(R0)to check whether the dialed number is valid
CJNE A,#000H,INCORRECT02 ;incorrect number
CJNE R0,#002H,CORRECT02 ;else dialed the same set number
LJMP NUMBER202 ;number 2 is dialed
CORRECT02: CJNE R0,#001H,NEXT02 ;if dialed number is not 1
LJMP NUMBER102 ;if dialed number is 1
NEXT02: CJNE R0,#003H,NEXT202 ;if not 3
LJMP NUMBER302 ;if dialed number is 3

NEXT202: LJMP NUMBER402 ;Therefore ultimate dialed number is 4

INCORRECT02: MOV P1,#098H ;dial tone
MOV R1,#010H
AGAIN4402: TIMER00 HIGH(DELAY_25ms),LOW(DELAY_25ms) ;call macro with high and low value of (-25000)

JNB P2.1,RESTART02 ;if set onhook
DJNZ R1,AGAIN4402 ;decrement and jump if not zero
MOV P1,#018H ;set dial tone to generate engage tone
MOV R1,#010H
AGAIN5502: TIMER00 HIGH(DELAY_25ms),LOW(DELAY_25ms) ;call macro with high and low value of (-25000)

JNB P2.1 ,RESTART02 ;if onhook
DJNZ R1,AGAIN5502 ;decrement and jump if not zero
LJMP INCORRECT02 ;else onhook

RESTART02: MOV P1,#018H ;remove engage tone
MOV R0,#000H ;reinitialize the pulse counter
LJMP WAITONHOOK02 ;resatart theprogram
NUMBER202: MOV R0,#000H ;reinitialize pulse counter
MOV P1,#018H
LJMP INCORRECT02
NUMBER102: CON_DIALNUMBER02 P0.0, RESTART02, 096H, P2.0, 016H,B.0
NUMBER302: CON_DIALNUMBER02 P0.2, RESTART02, 0A6H, P2.2, 026H,B.2
NUMBER402: CON_DIALNUMBER02 P0.3, RESTART02, 0AEH, P2.3, 02EH,B.3

WAITONHOOK02:JB P2.1,WAITONHOOK02 ;wait for onhook
TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)
JB P2.1,WAITONHOOK02 ;not valid onhook
LJMP WAITOFFHOOK02 ;jump to start

;*******************************SET3 CODE***************************************

WAITOFFHOOK03:JNB P2.2,$ ;check continuously whether the set is offhook
JB B.2,WAITOFFHOOK03 ;if already connected
MOV P1,#0A0H
MOV R1,#CONST ;initialize 5 sec counter
AGAIN03: TIMER00 HIGH(DELAY_25ms),LOW(DELAY_25ms) ;call macro with high and low value of (-25000)

JNB P2.2,PULSEDIALED03 ;if pulse dialed?
DJNZ R1,AGAIN03 ;decrement and jump if no t zero
MOV P1,#020H ;remove dial tone if no activity for 5 sec
LJMP WAITONHOOK03 ;wait for offhook again

PULSEDIALED03:MOV P1,#020H ;remove dialtone

LOW_PUSLEWIDTH_COUNTER03: MOV R1,#CONST ;200*250 usec=50 ms

AGAIN203: TIMER00 0FFH,006H ;call macro with high and low value of (-250)
JB P2.2,HIGH_PULSEWIDTH_COUNTER03 ;jump if valid pulse
DJNZ R1,AGAIN203 ;decrement and jump if not zero
MOV P1,#020H ;remove dial tone,not valid pulse, set is on hook
LJMP WAITOFFHOOK03 ;again check and wait for offhook
HIGH_PULSEWIDTH_COUNTER03: INC R0 ;count pulses

MOV R1,#CONST ;200*325usec= 65 msec
AGAIN303: TIMER00 0FEH,0BBH ;call macro with (-325)
JNB P2.2, LOW_PUSLEWIDTH_COUNTER03 ;pulse again
DJNZ R1,AGAIN303 ;decrement and jump if not zero

;DIALED NUMBER IS LOADED IN R0.NOW CHECK FOR VALID NUMBER

MOV DPTR,#0D00H ;laod base register in DPTR
MOV A,R0 ;laod dialed number in accumulator as offset
MOVC A,@A+DPTR ;laod the dialed number from lookup table by offset
CLR C ;in order to perfomr subtractionsuccesfully
SUBB A,R0 ;(A)<---- (A)-(R0)to check whether the dialed number is valid
CJNE A,#000H,INCORRECT03 ;incorrect number
CJNE R0,#003H,CORRECT03 ;else dialed the same set number
LJMP NUMBER303 ;number 3 is dialed

CORRECT03: CJNE R0,#001H,NEXT03 ;if dialed number is not 1
LJMP NUMBER103 ;if dialed number is 1
NEXT03: CJNE R0,#002H,NEXT203 ;if not 3
LJMP NUMBER203 ;if dialed number is 2
NEXT203: LJMP NUMBER403 ;Therefore ultimate dialed number is 4


INCORRECT03: MOV P1,#0A0H ;dial tone
MOV R1,#010H

AGAIN4403: TIMER00 HIGH(DELAY_25ms),LOW(DELAY_25ms) ;call macro with high and low value of (-25000)

JNB P2.2,RESTART03 ;if set onhook
DJNZ R1,AGAIN4403 ;decrement and jump if not zero
MOV P1,#020H ;set dial tone to generate engage tone
MOV R1,#010H

AGAIN5503: TIMER00 HIGH(DELAY_25ms),LOW(DELAY_25ms) ;call macro with high and low value of (-25000)

JNB P2.2 ,RESTART03 ;if onhook
DJNZ R1,AGAIN5503 ;decrement and jump if not zero
LJMP INCORRECT03 ;else onhook
RESTART03: MOV P1,#020H ;remove engage tone
MOV R0,#000H ;reinitialize the pulse counter
LJMP WAITONHOOK03 ;resatart theprogram
NUMBER303: MOV R0,#000H ;reinitializepulse counter
MOV P1,#020H
LJMP INCORRECT03
NUMBER103: CON_DIALNUMBER03 P0.0, RESTART03, 095H, P2.0, 015H,B.0
NUMBER203: CON_DIALNUMBER03 P0.1, RESTART03, 09DH, P2.1, 01DH,B.1
NUMBER403: CON_DIALNUMBER03 P0.3, RESTART03, 0ADH, P2.3, 02DH,B.3


WAITONHOOK03:JB P2.2,WAITONHOOK03 ;wait for onhook
TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)
JB P2.2,WAITONHOOK03 ;not valid onhook
LJMP WAITOFFHOOK03 ;valid offhook! restart...

;*******************************SET4 CODE***************************************

WAITOFFHOOK04:JNB P2.3,$ ;check continuously whether the set is offhook
JB B.3,WAITOFFHOOK04 ;if already connected
MOV P1,#0A8H
MOV R1,#CONST ;initialize 5 sec counter
AGAIN04: TIMER00 HIGH(DELAY_25ms),LOW(DELAY_25ms) ;call macro with high and low value of (-25000)

JNB P2.3,PULSEDIALED04 ;if pulse dialed?
DJNZ R1,AGAIN04 ;decrement and jump if no t zero
MOV P1,#028H ;remove dial tone if no activity for 5 sec
LJMP WAITONHOOK04 ;wait for offhook again

PULSEDIALED04:MOV P1,#028H ;remove dialtone

LOW_PUSLEWIDTH_COUNTER04: MOV R1,#CONST ;200*250 usec=50 ms

AGAIN204: TIMER00 0FFH,006H ;call macro with high and low value of (-250)
JB P2.3,HIGH_PULSEWIDTH_COUNTER04 ;jump if valid pulse
DJNZ R1,AGAIN204 ;decrement and jump if not zero
MOV P1,#028H ;remove dial tone,not valid pulse, set is on hook
LJMP WAITOFFHOOK04 ;again check and wait for offhook

HIGH_PULSEWIDTH_COUNTER04: INC R0 ;count pulses
MOV R1,#CONST ;200*325usec= 65 msec
AGAIN304: TIMER00 0FEH,0BBH ;call macro with (-325)
JNB P2.3, LOW_PUSLEWIDTH_COUNTER04 ;pulse again
DJNZ R1,AGAIN304 ;decrement and jump if not zero

;DIALED NUMBER IS LOADED IN R0.NOW CHECK FOR VALID NUMBER

MOV DPTR,#0D00H ;laod base register in DPTR
MOV A,R0 ;laod dialed number in accumulator as offset
MOVC A,@A+DPTR ;laod the dialed number from lookup table by offset
CLR C ;in order to perfomr subtractionsuccesfully
SUBB A,R0 ;(A)<---- (A)-(R0)to check whether the dialed number is valid
CJNE A,#000H,INCORRECT04 ;incorrect number
CJNE R0,#004H,CORRECT04 ;else dialed the same set number
LJMP NUMBER404 ;number 4 is dialed

CORRECT04: CJNE R0,#001H,NEXT04 ;if dialed number is not 1
LJMP NUMBER104 ;if dialed number is 1
NEXT04: CJNE R0,#002H,NEXT204 ;if not 2

LJMP NUMBER204 ;if dialed number is 2

NEXT204: LJMP NUMBER304 ;Therefore ultimate dialed number is 3

INCORRECT04: MOV P1,#0A8H ;dial tone
MOV R1,#010H
AGAIN4404: TIMER00 HIGH(DELAY_25ms),LOW(DELAY_25ms) ;call macro with high and low value of (-25000)

JNB P2.3,RESTART04 ;if set onhook
DJNZ R1,AGAIN4404 ;decrement and jump if not zero
MOV P1,#028H ;set dial tone to generate engage tone
MOV R1,#010H
AGAIN5504: TIMER00 HIGH(DELAY_25ms),LOW(DELAY_25ms) ;call macro with high and low value of (-25000)

JNB P2.3 ,RESTART04 ;if onhook
DJNZ R1,AGAIN5504 ;decrement and jump if not zero
LJMP INCORRECT04 ;else onhook
RESTART04: MOV P1,#028H ;remove engage tone
MOV R0,#000H ;reinitialize the pulse counter
LJMP WAITONHOOK04 ;resatart theprogram

NUMBER404: MOV R0,#000H ;reinitializepulse counter
MOV P1,#028H
LJMP INCORRECT04

NUMBER104: CON_DIALNUMBER04 P0.0, RESTART04, 094H, P2.0, 014H,B.0
NUMBER204: CON_DIALNUMBER04 P0.1, RESTART04, 09CH, P2.1, 01CH,B.1
NUMBER304: CON_DIALNUMBER04 P0.2, RESTART04, 0A4H, P2.2, 024H,B.2


WAITONHOOK04:JB P2.3,WAITONHOOK04 ;wait for onhook
TIMER00 HIGH(DELAY_50ms),LOW(DELAY_50ms) ;call macro with high and low value of (-50000)
JB P2.3,WAITONHOOK04 ;not valid onhook
LJMP WAITOFFHOOK04 ;valid offhook! restart...


;********************TIMER1 SERVICE ROUTINE (Scheduler)**********************

;This program assigns time slots to different sets's code
;It first save the status of the currently executing code
;Then laods the state of the next section of the code (for next set)
;This ISR executes in almost 90 cycles
;Requires approx. 7 Micro Secs to execute
;****************************************************************************


T1ISR: ;USING 3
SETB RS1
SETB RS0
CLR TR1 ;stop timer1
CLR TF1 ;clear timer1 overflow falg
MOV R1,018H ;R1<---R0

MOV @R1,A ;save accumulator
POP ACC ;pop PCH
INC R1 ;increment R1
MOV @R1,A ;save high byte of return address
POP ACC ;pop PCL
INC R1 ;increment R1
MOV @R1,A ;save low byte of return address
INC R1 ;increment R1
MOV @R1,IP ;save B
INC R1 ;increment R1
MOV @R1,TCON ;save timer control register
INC R1 ;increment R1
MOV @R1,TL0 ;save timer2 low byte
INC R1 ;increment R1
MOV @R1,TH0 ;save timer2 high byte
INC R1 ;increment R1
MOV @R1,00H ;save R0 of bank 0
INC R1 ;increment R1
MOV @R1,01H ;save R1 of bank 0
INC R1 ;increment R1
MOV @R1,02H ;save r2 of bank 0
INC R1 ;increment R1
MOV @R1,DPL ;save data pointer low byte
INC R1 ;increment R1
MOV @R1,DPH ;save data pointer high byte

MOV A,R0 ;move address of state of currently running set's process in A
ADD A,#0CH ;add 12 to jump to address of state of next set's process
CJNE A,#060H,LOAD ;if correct address load the state of next process
MOV A,#SET1 ;else laod state of first process(SET 1)

LOAD: MOV R0,A ;load the address of state of next process in R0.
ADD A,#0CH ;add 12 in accumulator
MOV R1,A ;load the address in R1
DEC R1 ;decrement R1
MOV DPH,@R1 ;get DPTR high value
DEC R1 ;decrement R1
MOV DPL,@R1 ;get DPTR low value
DEC R1 ;decrement R1
MOV 02H,@R1 ;get R2 of bank 0
DEC R1 ;decrement R1
MOV 01H,@R1 ;get R1 of bank 0
DEC R1 ;decrement R1
MOV 00H,@R1 ;get R0 of bank0
DEC R1 ;decrement R1
MOV TH0,@R1 ;get high value of timer0
DEC R1 ;decrement R1
MOV TL0,@R1 ;get low value of timer0
DEC R1 ;decrement R1
MOV TCON,@R1 ;get timer control register
DEC R1 ;decrement R1
MOV IP,@R1 ;get interrupt priority register
DEC R1 ;decrement R1
MOV A,@R1 ;get return address low byte in accumulator
PUSH ACC ;put return address low byte on stack
DEC R1 ;decrement R1
MOV A,@R1 ;get return adrress high byte in acc.
PUSH ACC ;put return address high byte on stack
DEC R1 ;decrement R1
MOV A,@R1 ;get accumulator back
MOV TH1,#0ECH ;put high value in timer
MOV TL1,#078H ;put low value in timer
CLR RS1 ;Clear register select bit1
CLR RS0 ;clear register select bit0
SETB TR1 ;start scheduling timer
RETI ;return from ISR

CSEG AT 0D00H ;reserved space for lookup tables
SETNUMBERS: DB 0,1,2,3,4 ;valid set numbers

END