pulse dialing detection code

can the following code be used with 8051 to detect pulse dialing from 100 to 110, if yes , please explain something about this code.
;
;===================================================
;
; EIGHT NUMBER
; TELEPHONE DIALER
;
; 6/2/92
;
;===================================================
; DIALER.ASM ---------------- is a program
; that stores 8 preselected telephone numbers
; inside EPROM memory. When selected by the
; grounding of any PORT1 pin, pulses out
; the chosen number with a normally closed
; 5V relay (driven by a 2N4402 transistor) connected
; to PORT3.2. Relay contacts are connected IN
; SERIES with either the RED or GREEN wires
; of an incoming telephone line.
;
; Dialer.Asm was designed around Suncoast Technologies'
; inexpensive 8031/51 based Single Board Computer.
; The 70691C can be purchased Assembled/Tested for
; $38.00 Or in kit form for only $27.00 (plus $3.00
; to cover the cost of US Priority Mail).
;
; Suncoast Technologies
; P.O. Box 5835
; Spring Hill, Florida 34606
; Voice/Fax (904) 596-7599
;
; VISA/MASTERCARD Accepted
;
; Use the A51 program to assembly the Dialer.Asm
; program. Type "A51 Dialer" <Enter>. Dialer.Obj
; will be created. Then take this .OBJ file and
; further convert it to .BIN using HEXBIN.COM
; Type "Hexbin Dialer.Obj" <Enter>. Dialer.Bin will
; be created. Take this .BIN file and "Burn" it into
; a standard 2764 EPROM. Place the now programmed
; 2764 EPROM into the IC3 location on the 70691C
; Single Board Computer. Install the relay, spring
; return switches ans 2N4402 Xsistor. Apply power.
; Short and PORT1 pin to ground; relay will Pulse
; Out the pre-programmed telephone number.
;
; --------------------------------------------------
;
.ORG h'0000
.EQU ESC,h'1B
MOV PSW,#h'0
MOV SCON,#h'5A
MOV TMOD,#h'10
MOV TCON,#h'54
SETB TR1
START: CLR A
MOV P1,#d'255
SETB P3.2
SETB P3.3
LP1: MOV A,P1
CJNE A,#d'255,HOLD
SJMP LP1
HOLD: MOV R5,#d'50
LCALL DELAY
AA: CJNE A,#d'254,BB
LJMP DIAL_1
BB: CJNE A,#d'253,CC
LJMP DIAL_2
CC: CJNE A,#d'251,DD
LJMP DIAL_3
DD: CJNE A,#d'247,EE
LJMP DIAL_4
EE: CJNE A,#d'239,FF
LJMP DIAL_5
FF: CJNE A,#d'223,GG
LJMP DIAL_6
GG: CJNE A,#d'191,HH
LJMP DIAL_7
HH: CJNE A,#d'127,II
LJMP DIAL_8
II: LJMP START
;
DIAL_1: LCALL XSTRING
;
; Place first tel. # in line JJ
;
; Format "x-xxx-xxx-xxxx OR
; "xxx-xxxx"
;
JJ: .DB "1-800-562-5725"
.DB ESC
LJMP START
DIAL_2: LCALL XSTRING
;
; Place second # in line KK
;
KK: .DB "1-714-259-7733"
.DB ESC
LJMP START
DIAL_3: LCALL XSTRING
;
; Place third # in line LL
;
LL: .DB "1-214-271-5546"
.DB ESC
LJMP START
DIAL_4: LCALL XSTRING
; Place fourth # in line MM
;
MM: .DB "596-8830"
.DB ESC
LCALL START
DIAL_5: LCALL XSTRING
;
; Place fifth # in line NN:
;
NN: .DB "1-313-744-1330"
.DB ESC
LCALL START
DIAL_6: LCALL XSTRING
;
; Place sixth # in line PP
;
PP: .DB "1-800-344-4539"
.DB ESC
LCALL START
DIAL_7: LCALL XSTRING
;
; Place seventh # in line QQ
;
QQ: .DB "1-800-826-5432"
.DB ESC
LCALL START
DIAL_8: LCALL XSTRING
;
; Place eight # in line SS
;
SS: .DB "596-6632"
.DB ESC
LCALL START
;
; Read Each Number
;
XSTRING:
CLR P3.3
POP DPH
POP DPL
XSTR_1: CLR A
MOVC A,@A+DPTR
XSTR_2: LJMP CONVERT
;
; Pulse out number
;
DIAL: CLR P3.2
MOV R5,#d'2
LCALL DELAY
SETB P3.2
MOV R5,#d'2
LCALL DELAY
DJNZ R0,DIAL
MOV R5,#d'15
LCALL DELAY
NEXT: INC DPTR
CLR A
MOVC A,@A+DPTR
CJNE A,#ESC,XSTR_2
MOV A,#1
JMP @A+DPTR
;
; Jump to read next digit
;
CONVERT:
;
; Convert Port1 ASCII character
; to decimal number & stroe in R0
;
CJNE A,#'-',DIGIT_1
LJMP NEXT
DIGIT_1:
CJNE A,#'1',DIGIT_2
MOV R0,#d'1
DIGIT_2:
CJNE A,#'2',DIGIT_3
MOV R0,#d'2
DIGIT_3:
CJNE A,#'3',DIGIT_4
MOV R0,#d'3
DIGIT_4:
CJNE A,#'4',DIGIT_5
MOV R0,#d'4
DIGIT_5:
CJNE A,#'5',DIGIT_6
MOV R0,#d'5
DIGIT_6:
CJNE A,#'6',DIGIT_7
MOV R0,#d'6
DIGIT_7:
CJNE A,#'7',DIGIT_8
MOV R0,#d'7
DIGIT_8:
CJNE A,#'8',DIGIT_9
MOV R0,#d'8
DIGIT_9:
CJNE A,#'9',DIGIT_0
MOV R0,#d'9
DIGIT_0:
CJNE A,#'0',RETURN
MOV R0,#d'10
RETURN: LJMP DIAL

END: SJMP END
;
; Delay loop for Pulse Train
; duration
;
DELAY: NOP
LOOP1: DJNZ R5,LOOP2
RET
LOOP2: MOV R6,#d'240
LOOP3: MOV R7,#d'90
DJNZ R7,*
DJNZ R6,LOOP3
LJMP LOOP1
.END