Architecture,
Assembly
Language,
And
Hardware
Interfacing
(Paperback)
SFR
Types
As
mentioned
in the
chart
itself,
the SFRs
that
have a
blue
background
are SFRs
related
to the
I/O
ports.
The 8051
has four
I/O
ports of
8 bits,
for a
total of
32 I/O
lines.
Whether
a given
I/O line
is high
or low
and the
value
read
from the
line are
controlled
by the
SFRs in
green.