User`s manual

XP8500 and Exp-A/D12100 s Technical Circuit Details
XP8500
Quad op-amp U2 buffers the four analog inputs received via Wago
connector H1. U2s four op-amp outputs go to the first four inputs of the
A/D converter U3s eleven analog inputs. The A/D converter, a TLC2543,
is a 12-bit, switched-capacitor, successive-approximation converter. The
A/D converters internal multiplexer samples and converts one input
channel at a time in response to commands received from the PLCBus.
The A/D converter sends converted data out serially. The converter also
receives commands serially. The A/D converter communicates via data
line DATAIN, clock line CLK, and chip-select line /ADSEL. Note that the
schematic shows these signals as DIN, CLOCK, and /ADCS, respec-
tivelyafter they pass through anti-latchup resistors R19R22. PAL U9
manages these lines by selecting U6s appropriate control-signal output
according to the state of PLCBus data lines D0D3. U6 has eight, single-
bit latches, each individually addressable.
Following the conversion period, the A/D converter shifts the resulting
digital data out one bit at a time through octal, noninverting bus driver
U5B and over the PLCBus to the controller. Also, the controller shifts in
one bit of a command word into the converter via the PLCBus and U6
(PAL U9 also controls U6) during each shift-clock period. This command
word specifies the converters next operation. Dynamic C library routines
take care of all the low-level details of communicating with the A/D
converter.
The protocol for controlling the serial A/D converter over the PLCBus is
complex. Z-World strongly recommends using the Dynamic C library
functions to control the converter.
Voltage Reference
The A/D converter chips two reference inputs, REF+ and REF-, establish
the voltage limits for analog inputs to produce the maximum and minimum
conversion values, respectively. Inputs higher than REF+ will return the
maximum conversion value while inputs less than REF- will return the
minimum conversion value.
Conversion Modes
The A/D converter operates in one of two conversion modes, absolute and
ratiometric, based on the jumper settings on headers J1 and J2 (see Figure
3-2). In the absolute-conversion mode, the A/D converter compares the
input signal being measured against an accurate and stable reference. The
ratiometric-conversion mode uses a reference derived from the analog
supply voltage. Ratiometric conversion suits signal voltages derived from,
or directly related to, the analog supply voltage such as a resistive sensor