User`s manual

XP8000 Series (PLCBus
TM
) Z-World 530-757-3737 6
Jumpers
The A/D12 board uses 4 jumpers, J1 through J4. Settings for J1,
coupled with the encoding of the PAL chip U7, determine the
board’s PLCBus address. These settings are explained later.
J1
Connect for address bit “x” = 0
Connect for address bit “y” = 0
Jumper J2 directs power for the board’s analog circuitry.
J2 V+ connected to VCC V+ connected to +5V from U10 J2
11
Jumper J3 is a write-protect switch for the EEPROM (U9).
J3
Write-protect Write-enable
1
J3
1
Jumper J4 routes a reference voltage to the A/D conversion chip
U4. The factory setting connects pins 2-3, routing U1’s preci-
sion 2.5V reference output to the A/D chip. Connecting pins 1-2
routes the “ratiometric” voltage (RM) to the A/D chip. (When
R7 = 0 and R3 is not installed, RM ≈ V+.)
J4
Route RM to A/D chip
1
Route precision + 2.5V to A/D chip
J4
1
The Analog Circuitry
The A/D12 board’s eight inputs (ANx+ and ANx–) are routed to
the board’s ADC chip by two analog multiplexers and several
differential amplifiers. Gains of 2, 6, 22, 42, 102, and 202X, as
well as unity gain, can be selected by software.
202X
EEPROM
AN[0-3]+
AN[0-3]
–
+
–
AN[4-7]+
AN[4-7]
–
+
–
MUX
MUX
IN+
IN
–
22X
42X
102X
6X
2X
CH0
CH1
G1
G2
G3
G4
G5
G6
REF+
+V Reg
–V Reg
VREF
+5V
–5V
+2.5V
Ratiometric Reference
+V
U11
U12
U4
CH2
CH3
CH4
CH5
CH6
CH7
ADC
The ADC Chip
The ADC chip, a 12-bit LTC1294, can convert a signal at one of
its input pins in either of two modes: unipolar or bipolar. The
chip’s allowable input range and output values are as follows:
Mode –Input Range –Output Range
Bipolar –2.5V to +2.5V –2048 to +2047
Unipolar –0 to +2.5V –0 to 4095
You can reduce a voltage input to the required range with a re-
sistor network. Otherwise, when an input voltage falls outside
the supported range, the chip responds with its maximum or
minimum value.
How to Use an A/D12 Board
Generally, this is what you do:
1 Initially, send a reset command to the PLCBus.
2 Place the address of the board on the PLCBus.
3 Read one of the A/D12 board’s input channels. Allow for
MUX settling time.
4 Calculate real-world values, such as temperature or dis-
placement, from the data obtained.
5 Use the data (to control relays, switches, or other devices).
Once an A/D channel has been set up, you can read it repeat-
edly, as fast as 165 µsec per read (on a 9 MHz controller).
Addressing the board
The address of a particular A/D12 board is determined (1) by the
encoding of PAL chip U7 installed on the board and (2) by
jumper J1. Sixteen different PALs are available and J1 can be
set four different ways, giving 64 unique addresses:
000p 10px ppRy
R = 0 for register S3A, 1 for register S3B
y = 1 when J1 pins 3-4 are not connected
x = 1 when J1 pins 1-2 are not connected
The bits pppp are determined by the PAL number.
For a given board, the R bit selects one of two hardware regis-
ters—S3A or S3B—coded on the PAL chip. S3A is a “MUX con-
trol register” that selects one of the board’s eight input chan-
nels. S3B is the “serial communication control register.”
The A/D12 expansion boards have logical addresses, 0–63, ac-
cording to this formula:
logical address = pppp × 4 + xy
where pppp, and y and x are defined above.
A/D Conversion Modes
When reading a differential input signal, connect the sensor to
both ANx+ and ANx–. When reading a single-ended signal, con-
nect the voltage source to ANx+ and connect ANx– to GND.
When reading a unity-gain single-ended signal, no ground is
necessary. Simply connect the voltage source to the desired ter-
minal (ANx+ or ANx–).
(When reading the A/D chip with Z-World software, specify the
desired gain and polarity by selecting a particular “A/D mode.”
There are 18 different A/D modes.)
Input Stability
Grounded input signals were used to calculate the standard de-
viations of “A/D channels.” Tests of 1000 samples per channel
were performed on typical boards in both unipolar and bipolar
modes. Under these conditions, the standard deviation for all
channels was under 1 part in 2047, and very near 0.1 part in
2047 for small gain values.
MUX Settling Time
When switching MUXs, you must allow the circuitry to settle
before attempting to read the A/D output. Capacitors C10–C14
(330 pF) attached to the feedback on gain amplifiers are the
greatest contributors of delay.
Reducing the size of the feedback capacitor reduces the settling
time, at the expense of noise filtering.