RabbitCore RCM2200, Руководство пользователя

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User’s Manual Hardware Reference 2–7
2.3 Other Hardware
2.3.1 Clock Doubler
The RabbitCore RCM2200 takes advantage of the
Rabbit 2000 microprocessor’s internal clock dou-
bler. A built-in clock doubler allows half-frequency
crystals to be used to reduce radiated emissions. The
22.1 MHz frequency is generated using an
11.0592 MHz crystal. The clock doubler is disabled
automatically in the BIOS for crystals with a fre-
quency above 12.9 MHz.
The clock doubler may be disabled if 22.1 MHz
clock speeds are not required. Disabling the Rabbit
2000 microprocessor’s internal clock doubler will
reduce power consumption and further reduce radi-
ated emissions. The clock doubler is disabled with a
simple change to the BIOS as described below.
2.3.2 Backup Battery Circuit
The RabbitCore RCM2200 does not have a battery,
but there is provision for a customer-supplied bat-
tery to back up SRAM and keep the internal Rabbit
2000 real-time clock running.
Header J5, shown in Figure 2–5, allows access to
the external battery. This header makes it possible to
connect an external 3 V power supply. This allows
the internal Rabbit 2000 real-time clock to run and
allows the SRAM to retain data when the Rabbit-
Core RCM2200 is powered down.
A lithium battery with a nominal voltage of 3 V and
a minimum capacity of 950 mA·h is recommended.
A lithium battery is needed because of its nearly
constant nominal voltage over most of its life.
The drain on the battery by the RabbitCore RCM2200
is typically 16 µA when no other power is supplied.
If a 950 mA·h battery is used, the battery can last
more than 6 years:
The actual life in your application will depend on
the current drawn by components not on the Rabbit-
Core RCM2200 and the storage capacity of the bat-
tery. Note that the shelf life of a lithium battery is
ultimately 10 years.
1.
Open the BIOS source code file,
RABBITBIOS.C
in the
BIOS
directory.
2.
Change the line
#define CLOCK_DOUBLED 1 // set to 1 to double the clock if XTAL<=12.9MHz,
to read as follows.
#define CLOCK_DOUBLED 0 // set to 1 to double the clock if XTAL<=12.9MHz,
3.
Change the serial baud rate to 57,600 bps when the RabbitCore RCM2200 is operated at 11.05
MHz.
4.
Save the change using File > Save .
Figure 2–5: External Battery Connections
at Header J5
D0
VCC
24
25
23
26
VBAT
GND
External
Battery
J5
950 mA·h
16 µA
------------------------
6.8 years. =