101-0568 Rabbit Semiconductor, 101-0568 Datasheet - Page 82

• Manufacturer Part Number: 101-0568
• Description: COMPUTER SNGLBD BL2100 512K FLSH
• Manufacturer: Rabbit Semiconductor

Specifications of 101-0568

• Module/board Type: Single Board Computer Module
• For Use With/related Products: BL2100
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

B.2.3 Power to VRAM Switch
The VRAM switch on the BL2100 module, shown in Figure B-3, allows the battery
backup to provide power when the external power goes off. The switch provides an isola-
tion between Vcc and the battery when Vcc goes low. This prevents the Vcc line from
draining the battery.
W
W
W
Figure B-3. VRAM Switch
Field-effect transistor Q5 is needed to provide a very small voltage drop between Vcc and
VRAM (<100 mV, typically 10 mV) so that the board components powered by Vcc will
not have a significantly different voltage than VRAM.
When the BL2100 is not in reset, the
line will be high. This turns on Q2, causing
/RESET
its collector to go low. This turns on Q5, allowing VRAM to nearly equal Vcc.
When the BL2100 is in reset, the
/RESET
line will go low. This turns off Q2 and Q5, pro-
viding an isolation between Vcc and VRAM.
B.2.4 Reset Generator
The BL2100 module uses a reset generator on the module, U1, 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.
76
Smartcat (BL2100)