| 摘要 |
PCT No. PCT/US81/00705 Sec. 371 Date May 27, 1981 Sec. 102(e) Date May 27, 1981 PCT Filed May 27, 1981 PCT Pub. No. WO80/02644 PCT Pub. Date Dec. 11, 1980.A power supply control circuit (20) selectively provides power to an integrated circuit from either a primary power supply terminal (22), or through terminals (24, 26) connected to backup batteries. The voltage level of the primary power is monitored continuously and when it drops to a predetermined level one of the two backup batteries is substituted to power the integrated circuit in a power-down mode. The circuit (20) includes a level detector circuit (32) and a voltage reference circuit (98). In the power-down mode one battery is connected to power the integrated circuit and this battery is continuously monitored. When the voltage of the on-line battery drops to below a fixed level in comparison to off-line battery a control logic circuit (92) activates switches (56) to substitute the off-line battery for the on-line battery. Control logic circuitry (92) is provided to disconnect the control signals from the integrated circuit to prevent loss of stored information. Further the failure of one of the backup batteries is indicated by disabling a write enable signal.
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