INTRODUCTION
The next higher order address lines,
A8
through A
15,
are present throughout the
machine cycle on both the
8088
and the
8085A. Note that the 8088 has four other
address lines, AI6 through AI9 not present
on
the 8085A and which the 8088 time-
multiplexes with status information during
the machine cycle.
The three control lines RD, WR, and 101M
signal the actual data transfer during a
machine cycle, whether the
8088
is
reading
or
writing, and whether that transfer
is
taking
place with respect to 110 devices
or
memory
8088
DT/R
devices. Also, the
8088,
like the 8085A, has
other lines containing cycle status infor-
mation available
at
the beginning of the
machine cycle to inform other devices in the
system what type
of
machine cycle
is
being
performed.
There are several other control lines used
with the
8088
such as interrupts, HOLD,
READY. See Chapter 3 for details.
Using Special Multiplexed Bus Parts
Because the
8088
is
so much like the 8085A,
you may connect the
8088
directly to a whole
family
of
multiplexed bus components de-
ADO-
AD7
AS-
A-15
ALE
101M
< >
.A
;
; 8085A
~
~
S1
STATUS .A
550
1--------,/
'I
SO
SOSSIS
AN
EASY
UPGRADE
FOR
EXISTING S-BIT SYSTEMS
Figure 1-22. 8088 Bus Interface is Similar to 8085
1-14