101-0492 Rabbit Semiconductor, 101-0492 Datasheet - Page 65

• Manufacturer Part Number: 101-0492
• Description: INTERFACE OP6800 W/ETHERNET PORT
• Manufacturer: Rabbit Semiconductor

Specifications of 101-0492

• Module/board Type: Single Board Computer Module
• For Use With/related Products: SR9160
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: 316-1060

B.2.2 Power to VRAM Switch
The VRAM switch on the OP6800 module, shown in Figure B-1, 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-1. 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 OP6800 is not in reset, the
/RESET
line will be high. This turns on Q2, causing
its collector to go low. This turns on Q5, allowing VRAM to nearly equal Vcc.
When the OP6800 is in reset, the
line will go low. This turns off Q2 and Q5, pro-
/RESET
viding an isolation between Vcc and VRAM.
B.2.3 Reset Generator
The OP6800 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.
User’s Manual
61