I want to convert the first of character each sentence to uppercase.For example i put in message1 then i change it.But i fail to run this program, so please help me recheck this program which is written in the TASM. Do you have any suggestion web sites about the TASM, assembly language, example, because i'm a beginner. Thank you..

;convert.asm
.model small
.stack 200h
.data
message1 Db 'i am a boy. you are a girl.'

.code
start:
mov ax, seg message1
mov ds, ax
cld
mov si, offset message1
call To_Uppercase
mov ah, 9
mov dx, offset message1
int 21h
To_Uppercase:
cmp byte ptr [si], '.'
je Done
mov [si-1], al
jmp To_Uppercase

Done:
lodsb
and al, 11011111b

Last:
mov ax,4c00h
int 21h
End start