Author :
Craig
Steiner
Source :
8052.com
Book :
The
8051/8052
Microcontroller:
Architecture,
Assembly
Language,
And
Hardware
Interfacing
(Paperback)
The TCON SFR
Finally,
there’s
one more
SFR that
controls
the two
timers
and
provides
valuable
information
about
them.
The TCON
SFR has
the
following
structure:
TCON
(88h)
SFR
Bit |
Name |
Bit Address |
Explanation of Function |
Timer |
7 |
TF1 |
8Fh |
Timer 1 Overflow. This bit is set by the microcontroller when Timer 1 overflows. |
1 |
6 |
TR1 |
8Eh |
Timer 1 Run. When this bit is set Timer 1 is turned on. When this bit is clear Timer 1 is off. |
1 |
5 |
TF0 |
8Dh |
Timer 0 Overflow. This bit is set by the microcontroller when Timer 0 overflows. |
0 |
4 |
TR0 |
8Ch |
Timer 0 Run. When this bit is set Timer 0 is turned on. When this bit is clear Timer 0 is off. |
0 |
As you may notice, we’ve only defined 4 of the 8 bits.
That’s
because
the
other 4
bits of
the SFR
don’t
have
anything
to do
with
timers--they
have to
do with
Interrupts
and they
will be
discussed
in the
chapter
that
addresses
interrupts.
A new
piece of
information
in this
chart is
the
column
"bit
address."
This is
because
this SFR
is
"bit-addressable."
What
does
this
mean? It
means if
you want
to set
the bit
TF1--which
is the
highest
bit of
TCON--you
could
execute
the
command:
MOV
TCON,
#80h
... or, since the SFR is bit-addressable, you could just
execute
the
command:
SETB TF1
This has the benefit of setting the high bit of TCON
without
changing
the
value of
any of
the
other
bits of
the SFR.
Usually
when you
start or
stop a
timer
you
don’t
want to
modify
the
other
values
in TCON,
so you
take
advantage
of the
fact
that the
SFR is
bit-addressable.
<<< Click
here to
come
back on
(8051
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