DS5000FP datasheet(7/22 Pages) DALLAS

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DS5000FP

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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 VLI as a reference in determining the switch

points. These are called VPFW, VCCMIN, and VLI respectively. When VCC drops below VPFW, 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 VCCMIN, the DS5000FP invokes a reset state.

No further code execution will be performed unless power rises back above VCCMIN. CE1 , CE2 , R/ W go

to an inactive (logic 1) state. Any address lines that are high (due to encryption) will follow VCC, except

for BA14, which is lithium backed. VCC is still the power source at this time. When VCC drops further to

below VLI, 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. VCCO 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:

VPFW = 1.45 x VLI

VCCMIN = 1.40 x VLI

VLI Switch = 1.0 x VLI

MEMORY MAP OF THE DS5000FP Figure 2

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