Serial
Data
Chain
(Part
of
0
0)
The
2212 is fully microprocessor controlled. To prevent digital noise,
glitches
and
other polluted signals that can disturb
the
sensitive circuitry of
the scope, the microprocessor controls the analog section of
the
scope
by
way
of
a serial data chain.
There is
no
system bus activity or other microprocessor activity on the
mainboard of the 2212 oscilloscope. Six bytes are required to set
up
the
analog part of the scope.
Byte
1.
Byte
2.
Byte
3.
Byte
4.
Byte
5.
Byte
6.
U800 contains the control byte for the trigger source- coupling-
and
slope selection.
U801 contains the controlbyte
for
the trigger
mode
that
sets the
sweep logic.
U802 contains the controlbyte for
the
sweep speed.
U803 contains the controlbyte
for
the
CH
1 sensitivity.
U804 contains the controlbyte
for
the
CH
2 sensitivity.
U805 contains the control byte
for
the vertical
mode
selection.
The six single shift registers are cascaded to one 48 bit long shift register,
called the data chain. When new data must be shifted into the chain, the
microprocessor places bit
by
bit on
the
serial data line (SER_DAT
A)
and
shifts it into the chain with the serial clock signal
(SER_CLK).
The
shift
registers are not transparent, so a bit that is moving through
the
chain
does
not affect
the
outputs. When the 48 bits word is loaded, a strobe pulse
(CHAIN_LD)
clocks all bits
in
parallel to their outputs. If one
bit
of the
chain has to be changed, a complete
new
48 bits
wide
word
must
be loaded
into the chain.
Daculator
Circuit
The
2212 scope has a 16 channel DAC, called the daculator.
The
outputs of
this
DAC
are used to control and calibrate the scope.
The
individual out-
puts are discussed in other parts of
the
circuit description.
The
daculator is
loaded the same way as the serial data chain
with
a 16 bits
wide
word.
3 -
18
12
Bits for
the
DAC
and 4 bits to address the
output
channel.
The
daculator uses the same serial data line (SER_DA TA) and
the
same
clock signal
(SER_CLK)
and has its own strobe pulse,
(DACU_LD).
So all
the code information is loaded into both shift registers, the serial data
chain
and the daculator. The
CHAIN_LD
and the DACU_LD pulse however
determine which circuit actually accepts the data.
The daculator is completed with some peripheral circuitry to improve the
performance.
An
external reference is used to have a better accuracy and
lower drift.
An
RC
filter and a buffer circuit at each
output
are provided to
reduce digital noise and increase the output drive.
Theory
of
Operation
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