2212 Service Manual
Digital Circuitry
The data
needed
for
writing the data to the screen is all directly read from the
68070 microprocessor memory using DMA (Direct Memory Access). To
perform
this
task, the highest priority DMA channel of the internal
DMA
controller is used (in burst mode). To get a constant flow
of
display data, the
display system is coupled
to
the microprocessor bus through a first-in/first-
out buffer (FIFO) with a depth of 16 words (U1900 - U1905).
The
16
bits of data from the databus are directed to the DAC's U1922 and
Ul
923, to generate analog signals. In this way readout positioning can be
performed
with
a resolution of 256 x 256 pixels. To get the full performance
needed to get all the features generating the 2212 display, the display system
is made "programmable"
by
adding a readout control byte
(RC0
-
RC7
from
Ul
906).
This
byte is fed into the FIFO's synchronously with the display data
and can
be
set by the microprocessor to select
the
type of display function
needed.
The main functionality of the display system is determined
by
the 22V10
PAL U1925
in
combination with counter U1932.
The
PAL,
also controlled by the readout controlbyte, determines the timing of
the display process and generates the digital signals needed for the analog
mainboard (clocked by the
CLK5M
timing signal).
In combination with the 74HC592 counter U1932, longer timing periods can
be generated. In this way magnification of waveforms can be performed
by
stretching
the
display time of one acquisition-dot, times
ten
or times fifty.
The following analog circuitry is added to get more resolution than the 256
positions provided by the 8 bit DAC's:
- An analog sweep generator
for
displaying the 4096 position waveforms
horizontally (U1600A and C1903). Displaying readout data will
automatically reset the sweep generator.
A "dwell" control is provided to stop the waveform during display when
a trigger
point
is written or a store mode time cursor.
Two 12 bits daculator outputs
REFCUR
and
DELTACUR for the
positioning of the voltage and time cursors
in
analog mode
and
the voltage
cursors
in
store mode.
The analog multiplexers U1930
and
U1931 (also controlled by the readout
controlbyte), determine which signal is routed to the analog outputs
ROHOR
andROVERT.
Readout control bytes are used as stated
in
Table 3-2.
3-
23
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