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APPLICATION EXAMPLES
Any memory reads using addresses 1030H-
17FFH will simultaneously cause a write to
the 8276 row buffers (Fig.
4-9).
In
this way, the iAPX
88
emulates
DMA
by
addressing both the
8185s
and
8276,
directly
transferring data from the screen memory to
the 8276 row buffers. Other accesses of screen
memory, such as inputting a character from
the keyboard, are done using addresses
between
30H and 7FFH.
Another demonstration of the power of the
iAPX
88
is
the routine which recognizes
escape characters (Fig. 4-10).
Using the iAPX 88's Translate (XLAT)
instruction and flexible addressing, this
routine takes only 9 lines and
22
bytes of
code.
It
executes in 6.6 microseconds. This
same routine written for the
8085A-2 takes
20
8088
lines,
61
bytes, and
31
microseconds. The
iAPX
88
uses fewer than half the lines and
bytes of code, while executing 4.7 times
faster!
iAPX 88 MULTIPROCESSING SYSTEMS
Using multiple processors in medium-to-
large systems offers several significant advan-
tages over the centralized approach that relies
on a single
CPU
and extremely fast memory:
1) System tasks may be allocated to special-
purpose processors whose designs are opti-
mized to perform specific tasks simply and
efficiently.
2)
Very high levels of performance can be
attained when processors can execute simul-
taneously (parallel/ distributed processing).
DATA
BUS
DATA FLOW
RDr-----------------------~~
1/2
'--
74LS139
Yr-~~------------~~
ADkr.
...
D_E_C_O_D_E_R
...
BUS
, G
112
74LS139
o--s
0---
DECODER o--s
A SINGLE 8088 STRING INSTRUCTION
MOVES
DATA BYTES FROM THE 8185
RAM
TO THE 8276 ROW BUFFER. THE
8088
"THINKS"
IT IS LOADING THE
AX
REGISTER.
1
BS
WR
L----o
CS
CRT
CONTROLLER
8276
Figure 4-9. 8276 Row
Buffer
Loading
4-16
CS
RD
SCREEN
MEMORY
8185