Maxim Integrated High-Speed Microcontroller - Manual (Page 162)

High-Speed Microcontroller User’s Guide
Rev: 062210 162 of 176
Backup current is a function of temperature, and therefore battery life is dependent on the operating
environment.
The registers shown in
Table 15-B are battery-backed, and one or more bits will be indeterminate
following a no-battery reset. They should be initialized as part of a no-battery reset procedure.
Table 15-B. Battery-Backed SFRs
REGISTER NAME LOCATION
TRIM 96h
RTASS F2h
RTAS F3h
RTAM F4h
RTAH F5h
RTCC F9h
RTCSS FAh
RTCS FBh
RTCM FCh
RTCH FDh
RTCD0 FEh
RTCD1 FFh
15.2 Lithium Battery Considerations
Lithium primary (nonrechargeable) batteries can fail and/or rupture if subjected to reverse current from
the device they are powering. The battery-switching circuitry inside the DS87C530 was designed to
reduce or eliminate the need for external hardware required to meet battery safety regulations. As shown
in the DS87C530 data sheet, a current-limiting resistor is always in series with a switching field-effect
transistor, regardless of whether the DS87C530 is drawing current from V
CC
or V
BAT
pins. This satisfies
the two-mechanism requirement of most safety codes.