Hello. Plz run the program on KEIL uVision2 & suggest me.

1. This program is for sending "M" to computer hyperterminal 20 times.

2. Serial Interrupt is activated

3. When running the program line by line, during "jnb ti,$" instruction execution, if i press some thing from key board then RI is activated & execute the ISR & sends the received data to P1. And finishing execution of ISR it returns to the same "jnb ti,$".

4. My problem is, at the time of transmiting "M" is loaded in SBUF reg. At the same time if RI is activated and loads the received data to sbuf, then why sbuf value is not changed on simulator.

5. It is doing transmitting & receiving at a time. Having one SBUF reg, how it is doing both the jobs.

PLZ clear this to me.

org 00h
sjmp main

org 23h
sjmp serial

org 30h
main:
mov tmod,#20h
mov th1,#0fdh
mov scon,#50h
mov ie,#10010000b
mov r0,#20
setb tr1
back:
acall ser
djnz r0,back
sjmp $

serial:
jb ti,trans
mov a,sbuf
mov p1,a
clr ri
reti
trans:
reti

ser:
mov sbuf,#'M'
jnb ti,$
clr ti
ret
end

 

5. It is doing transmitting & receiving at a time. Having one SBUF reg, how it is doing both the jobs.

SBUF is not a single register, instead it is two registers with the same name.

One of them takes care of the data to be transmitted and the other holds the data received.

So when you write to SBUF, it is not the same as read from SBUF.