Fluke PM6681 - Page 42

GPIB
Interface
Figure
4-23
GPIB
interface.
The
GPIB
interface
controls
the communication
between
the internal microprocessor
and
the external GPIB bus,
(see Figure 4-23).
Communication between the
GPiB
control
circuit,
U78,
and
the
external
GPIB bus is done via the
bi-directional
bus
drivers
U79
and U80. U78 is controlled from
the micro-
processor by
writing
and reading in the internal
control regi-
sters. if U78 has a
message
for the microprocessor,
it
uses the GPIB
interrupt
signal. The address of the
GPIB
bus is software
controlied.
U9
to U13 are the
RAM
used to execute
the program. U14
and
U15 are
address
iatches.
Analog Output
Figure
4-24
Analog output
he
resuit
on
the display can
be
converted to an
analog si-
gnal. A
digital pulse width
modulated signal,
PWM, from
the
microprocessor is
fiitered
and integrated {U77)
to give
an
analog
DC ievei between
0 and 4.98 V
with
a resolution
of 20
mV,
(see Figure
4-24).
4-18
Hardware
Functional
Description