20-101-0356 Rabbit Semiconductor, 20-101-0356 Datasheet - Page 30

• Manufacturer Part Number: 20-101-0356
• Description: COMPUTER SINGLE-BOARD BL1800
• Manufacturer: Rabbit Semiconductor

Specifications of 20-101-0356

• Module/board Type: Single Board Computer Module
• Product: Modules
• Data Bus Width: 8 bit
• Processor Type: Rabbit 2000
• Sram: 128 KB
• Flash: 256 KB
• Timers: 8 bit, 10 bit
• Number Of I/os: 14
• Backup Battery: 3 V Lithium Coin Type
• Operating Voltage: 8 V to 40 V
• Power Consumption: 1.2 W
• Board Size: 89 mm x 64 mm x 19 mm
• Description/function: Computer Module
• For Use With/related Products: BL1800
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 316-1079

3.4.2 DA0
The op amp supporting DA0 translates a 12%–88% duty cycle to an analog voltage range
of 0 V to 3 V. The software operates only within this duty cycle; a duty cycle less than
12% is rounded down to 0%, and any duty cycle above 88% is rounded up to 100%.
DA0 uses a voltage divider that consists of R21 and R27 and a gain-offset circuit that con-
sists of R26 and R29 to achieve the output range of 0 V to 3 V within the software duty
cycle.
The DA0 output can be less than 100 mV for a 0% duty cycle and above 3.0 V for a 100%
duty cycle. The duty cycle is programmed as the high-time count of 1024 total counts of
the Rabbit 2000’s timer B. Thus, 256 counts would be 25% of 1024 counts, and corre-
sponds to a 25% duty cycle.
Table 3 lists typical DA0 voltages measured for various duty cycle values with a load
larger than 1 MΩ.
It is important to remember that the DA0 output voltage will not be realized instantaneously
after programming in a value. There is a settling time because of the RC time constant
(R21 || R27 × C20), which is 7.68 ms. For example, the voltage at any given time is
where V is the voltage at time t, V
put voltage from the D/A converter, and RC is the time constant (7.68 ms). The settling
will be within 99.326% (or within about 21 mV for a 3 V change in voltage) after five time
constants, or 38 ms. Six time constants, 46 ms, will allow settling to within 99.75% (or to
within about 8 mV for a 3 V change in voltage). Seven time constants, 54 ms, will allow
settling to within 99.91% (or to within about 3 mV for a 3 V change in voltage).
The settling time is reduced somewhat by precharging capacitor C20 with pulse-width
modulation from PD2.
26
Table 3. Typical DA0 Voltages for Various Duty Cycles
Duty Cycle
100
(%)
12
25
50
75
88
0
V = V
P
P
is the programmed voltage, V
– (V
P
Voltage
– V
0.074
0.076
0.530
1.467
2.406
2.875
3.345
(V)
DA0
)e
(-t/RC)
Programmed Count
902–1024
0–122
123
256
512
768
901
DA0
is the last DA0 out-
Jackrabbit (BL1800)
(EQ 2)