Rabbit 2000 Getting Started - page 23
18
Rabbit 2000 Development Kit
is operating at 32.768 kHz. The interrupt routine cannot complete at this slow speed
before the next tick of the periodic interrupt. In this situation, the hardware real-time
clock can be read directly to provide the time.
•
Watchdog support routines. Although the Rabbit watchdog can be disabled, this is not
recommended since the watchdog is an essential facility for recovering from crashes.
Very few systems are crash-free in real life.
4.2 I/O Drivers
The Jackrabbit board contains four high-power digital output channels, two D/A converter
output channels, and one A/D converter input channel. These I/O channels can be
accessed using the functions found in the
JRIO.LIB
library.
4.2.1 Initialization
The function
jrioInit()
must be called before any other function from the
JRIO.LIB
library. This function initializes the digital outputs and sets up the driver for the analog
input/outputs. The digital outputs correspond to the Rabbit processor’s port E bits 0–3,
and the analog I/O uses timer B; bits 1, 2, and 4 of port D; and bits 6 and 7 of port E.
The function void
jrioInit()
initializes the I/O drivers for Jackrabbit. In particular, it
sets up parallel port D bits 1, 2, and 4 for analog output, port E bits 0–3 for digital output,
and starts up the pulse-width modulation routines for the A/D and D/A channels. Note
that these routines can consume up to 20% of the CPU’s processing power; the routines
use timer B and the B1 and B2 match registers.
4.2.2 Digital Output
The Jackrabbit board contains four high-power digital output drivers, HV0–HV3, on
header J4. These can be turned on and off with the following functions from the library
JRIO.LIB
.
HV0, HV1, and HV2 are open-collector sinking outputs, and are able to sink up to 1 A
(200 mA for the BL1810 and BL1820) from a 30 V source connected to the K line on
header J4. HV3 is a sourcing output that is
able to source up to 500 mA (100 mA for the
BL1810 and BL1820) from a 30 V source
connected to the K line.
Remember to cut the trace between K and
Vcc inside the outline for header JP2 on the
top side of the Prototyping Board if you are
supplying K from a separate power sup-
ply. An exacto knife, a precision grinder
tool, or a screwdriver may be used to cut
through the traces as shown in Figure 5.
Failure to do this could lead to the destruc-
tion of the Rabbit 2000 microprocessor and
other components once the Jackrabbit is
connected to the Prototyping Board.
Figure 5. Cut Trace on Prototyping Board
When Vcc and K Are Different
Cut gray trace
as shown
Cut
Buzzer
Top Side
Prototyping
Board
JP2
1
2
3
R3
R1
LS1
RT
1
BZR
VCC
K
AD0
PE4
POT
HV0 +RAW
COIL(-)
PD0
GND
AD0
+
JP2
K
VCC