101-0788 Rabbit Semiconductor, 101-0788 Datasheet - Page 74

• Manufacturer Part Number: 101-0788
• Description: COMPUTER SGL-BOARD OP6600 W/SRAM
• Manufacturer: Rabbit Semiconductor

Specifications of 101-0788

• Module/board Type: Single Board Computer Module
• For Use With/related Products: OP6600
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: 101-788; 101-788

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Figure C-4. VRAM Switch
Transistor Q3 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 Intellicom is not resetting (pin 2 on U4 is high), the /RES line will be high. This
turns on Q4, causing its collector to go low. This turns on Q3, allowing VRAM to nearly
equal Vcc.
When the Intellicom is resetting, the /RES line will go low. This turns off Q3 and Q4, pro-
viding an isolation between Vcc and VRAM.
The battery-backup circuit keeps VRAM from dropping below 2 V.
C.2.3 Reset Generator
The Intellicom uses a reset generator, U2, 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.
C.2.4 Replacing the Backup-Battery Board
The pluggable backup-battery board makes it easy to replace the backup battery with a
fresh backup battery on another backup battery board. Before replacing the backup-battery
board, make sure that the Intellicom is receiving power from the standard power supply.
This makes sure that data in RAM are not lost when the battery-backup board is removed
temporarily.
To replace the backup-battery board, remove the screw and unplug the old battery board as
shown in Figure C-5.
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Intellicom (OP6600/OP6700)