DS5000FP_05 Datasheet, PDF (7/22 Pages) Dallas Semiconductor – Soft Microprocessor Chip

DS5000FP
POWER MANAGEMENT
The DS5000FP monitors power to provide Power-Fail Reset, early warning Power-Fail Interrupt, and
switchover to lithium backup. It uses the lithium cell at V_LI as a reference in determining the switch
points. These are called V_PFW, V_CCMIN, and V_LI respectively. When V_CC drops below V_PFW, the DS5000FP
will perform an interrupt vector to location 2Bh if the power-fail warning was enabled. Full processor
operation continues regardless. When power falls further to V_CCMIN, the DS5000FP invokes a reset state.
No further code execution will be performed unless power rises back above V_CCMIN. CE1 , CE2 , R/ W go
to an inactive (logic 1) state. Any address lines that are high (due to encryption) will follow V_CC, except
for BA14, which is lithium backed. V_CC is still the power source at this time. When V_CC drops further to
below V_LI, internal circuitry will switch to the lithium cell for power. The majority of internal circuits will
be disabled and the remaining nonvolatile states will be retained. The lithium cell will power any devices
connected to VCCO at this time. V_CCO will be at the lithium battery voltage less a diode drop. This drop
will vary depending on the load. Low-leakage SRAMs should be used for this reason. When a module is
used, the lithium cell is selected by Dallas so absolute specifications are provided for the switch
thresholds. When using the DS5000FP, the user must select the appropriate battery. The following
formulas apply to the switch function:
V_PFW = 1.45 x V_LI
V_CCMIN = 1.40 x V_LI
V_LI Switch = 1.0 x V_LI
MEMORY MAP OF THE DS5000FP Figure 2
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