User`s manual

XP8000 Series (PLCBus
TM
) Z-World 530-757-3737 11
Jumpers
The DAC8 board uses 3 jumpers, H1 through H3 to select the
±12V source:
Internal ± 12V
1
H1
1
H2
H3
External ± 12V
1
H1
1
H2
H3
EEPROM
The DAC8 board’s EEPROM (U5) stores calibration constants
and is controlled by the CPLD (U1).
CPLD
The DAC8 board’s CPLD (U1) encapsulates the board’s logic. It
monitors PLCBus addresses to determine if the board is being
addressed. When the board is being addressed, the CPLD exam-
ines the low 2 bits of the address. These 2 bits identify the cur-
rent DAC8 operation:
Bits Mode Description
00 DAC Write to a selected DAC. Bit 0 of BUSWR is
for data; bit 1 clocks the data.
01 EE Read or write the EEPROM.
BUSWR: Bit 0 = data; bit 1 = clock.
BUSRD0: Bit 0 = data.
10 Select BUSWR: when data = 0111, turn on 2V ref.
BUSWR: when data = 0110, turn off 2V ref.
BUSWR: when data = 1xxx, turns on channel
xxx (0–7).
BUSRD0: reads 1010 when board is present.
The CPLD can enable or disable DAC output (by turning on and
off the 2V reference).
The AD5320 Chip
The AD5320 is a single 12-bit DAC operating from a single 2.7–
5.5V supply. It has an on-chip output amplifier that allows true
rail-to-rail output swing. Its reference is derived from the
power input. Its output is guaranteed monotonic.
The AD5320 sinks/sources 140 µA at 5V during normal opera-
tions and 200 nA in power-down mode. There are three power-
down modes; the differences between them are not relevant.
Each of the eight AD5300s receives serial data in a 16-bit shift
register. Two bits represent “power-down mode” (normal mode
is 0). The low 12 bits represent the output value:
15 0
Power Down Mode
PD
13 11
data bits
Following the 16-bit sequence, the CPLD strobes the DAC chip.
The output of each DAC is given by the following formula:
V
OUT
= V
REF
× ( input / 4096 )
where V
REF
is +5V from U2.
Bipolar and Unipolar Operation
The AD5320 was designed for unipolar operation, but with an
op-amp and the right resistors, bipolar output can be achieved.
The default output for the XP8900 is bipolar. The formula for
output on the XP8900 is
V
OUT
= V
REF
×
4096
input
R
1
R
1
+ R
2
× – 2 ×
R
1
R
2
The XP8900 has, by default, R1 = 100K (two 200K resistors in
parallel) and R2 = 410K (two 205K resistors in series). Thus,
100
V
OUT
= 5 ×
4096
input
× – 2 ×
100
100 + 410410
= 20.5 ×
4096
input
–
10.2
giving a full range from –10.2V to +10.3V:
+10.3
0
–10.2
0 4095
Digital Input
Voltage Output
How to Use a DAC8 Board
Generally, this is what you do:
1 Initially, send a reset command to the PLCBus.
2 Place the address of the DAC8 board on the PLCBus. The
low two bits of the address select the type of operation as
described previously.
3 Carry out a read or write. Some details follow.
4 Use the analog output (to control motors or other analog
devices).
Addressing the board
Up to 8 DAC8 boards may be addressed individually over a
single PLCBus. The address of a particular DAC8 board is deter-
mined by 3 jumpers at P3. The address bits are:
0010 000z yxMM
z = 1 when P3 pins 1-2 are not connected
y = 1 when P3 pins 3-4 are not connected
x = 1 when P3 pins 5-6 are not connected
The bits MM determine the DAC8 operation, as described previ-
ously
. Software gives DAC8 expansion boards logical addresses,
0–7, according to the formula:
logical address = zyx
where zyx = 7 (no jumpers) is the default.