20-101-0383 Rabbit Semiconductor, 20-101-0383 Datasheet - Page 69

• Manufacturer Part Number: 20-101-0383
• Description: MODULE RABBITCORE RCM2020
• Manufacturer: Rabbit Semiconductor

Specifications of 20-101-0383

• Module/board Type: MPU Core Module
• Product: Microcontroller Modules
• Core Processor: Rabbit 2000
• Clock Speed: 18.432 MHz
• Interface Type: Ethernet, Serial
• Flash: 256 KB
• Timers: 5 x 8 bit, 2 x 10 bit
• Operating Supply Voltage: 4.75 V to 5.25 V
• Board Size: 48.3 mm x 58.4 mm x 14 mm
• Core: RCM2020
• Processor Series: RCM2000
• For Use With/related Products: RCM2020
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 316-1082

C.1.3 Power to VRAM Switch
The VRAM switch, shown in Figure C-3, allows a customer-supplied external battery to
provide power when the external power goes off. The switch provides an isolation
between Vcc and the battery when Vcc goes low. This prevents the Vcc line from draining
the battery.
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Figure C-3. VRAM Switch
Transistor Q11 is needed to provide a very small voltage drop between Vcc and VRAM
(<100 mV, typically 10 mV) so that the processor lines powered by Vcc will not have a
significantly different voltage than VRAM.
When the RCM2000 is not resetting (pin 2 on U10 is high), the /RES_OUT line will be
high. This turns on Q10, causing its collector to go low. This turns on Q11, allowing
VRAM to nearly equal Vcc.
When the RCM2000 is resetting, the /RES_OUT line will go low. This turns off Q10 and
Q11, providing an isolation between Vcc and VRAM.
The battery-backup circuit keeps VRAM from dropping below 2 V.
C.1.4 Reset Generator
The RCM2000 uses a reset generator, U10, to reset the Rabbit 2000 microprocessor when
the voltage drops below the voltage necessary for reliable operation. The reset occurs
between 4.50 V and 4.75 V, typically 4.63 V. The RCM2000 has a reset output, pin 37 on
header J3, presented to the headers. The reset generator has a reset input, pin 38 on header
J3, that can be used to force the RCM2000 to reset.
User’s Manual
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