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X4003S8I-2.7 Datasheet(PDF) 3 Page - Xicor Inc. |
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X4003S8I-2.7 Datasheet(HTML) 3 Page - Xicor Inc. |
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3 / 18 page  X4003/X4005 Characteristics subject to change without notice. 3 of 18 REV 1.1.3 4/30/02 www.xicor.com PRINCIPLES OF OPERATION Power On Reset Application of power to the X4003/X4005 activates a power on reset circuit that pulls the RESET/RESET pin active. This signal provides several benefits. – It prevents the system microprocessor from starting to operate with insufficient voltage. – It prevents the processor from operating prior to stabilization of the oscillator. – It allows time for an FPGA to download its configura- tion prior to initialization of the circuit. When VCC exceeds the device VTRIP threshold value for 200ms (nominal) the circuit releases RESET/ RESET, allowing the system to begin operation. Low Voltage Monitoring During operation, the X4003/X4005 monitors the VCC level and asserts RESET/RESET if supply voltage falls below a preset minimum VTRIP. The RESET/RESET signal prevents the microprocessor from operating in a power fail or brownout condition. The RESET/RESET signal remains active until the voltage drops below 1V. It also remains active until VCC returns and exceeds VTRIP for 200ms. Watchdog Timer The watchdog timer circuit monitors the microproces- sor activity by monitoring the SDA and SCL pins. The microprocessor must toggle the SDA pin HIGH to LOW periodically, while SCL also toggles from HIGH to LOW (this is a start bit) followed by a stop condition prior to the expiration of the watchdog time out period to pre- vent a RESET/RESET signal. The state of two nonvol- atile control bits in the control register determine the watchdog timer period. The microprocessor can change these watchdog bits, or they may be “locked” by tying the WP pin HIGH. Figure 1. Watchdog Restart SCL SDA .6µs .6µs Start Condition Stop Condition Restart Set VTRIP Level Sequence (VCC = desired VTRIP value) 012 45 67 SCL SDA A0h 012 345 67 01h WP VP = 15-18V 012 345 67 00h 3 VCC THRESHOLD RESET PROCEDURE The X4003/X4005 is shipped with a standard VCC threshold (VTRIP) voltage. This value will not change over normal operating and storage conditions. How- ever, in applications where the standard VTRIP is not exactly right, or if higher precision is needed in the VTRIP value, the X4003/X4005 threshold may be adjusted. The procedure is described below, and uses the application of a nonvolatile control signal. Setting the VTRIP Voltage This procedure is used to set the VTRIP to a higher voltage value. For example, if the current VTRIP is 4.4V and the new VTRIP is 4.6V, this procedure will directly make the change. If the new setting is to be lower than the current setting, then it is necessary to reset the trip point before setting the new value. |
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