There important cases initial voltage considerations that system desig

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CY7C634XX CY7C635XX Keyboard Families: Power-On Reset Considerations
There important cases initial voltage considerations that system designer using Keyboard Microcontroller must aware plan for. These are: slow voltage rise during cold power-up host fast voltage rise during hot-plugging into already stable bus. Keyboard families have built-in circuitry that resets Microcontroller during initial voltage ramp. This internal circuitry accommodate voltage ramp rates between able differentiate between these four decades variation. correct sequence hot-plug event follows: Microcontroller experiences ramp (which must constrained greater than µs). Port logic high with respect during voltage ramp (see next section). traffic occurs after ramp device goes into suspend. Reset takes device suspend Microcontroller begins reset vector. Device awaits enumeration loss keep-alive. other Microcontroller families immediately into suspend after Power-On-Reset event (POR), however, 7C634XX/5XX families have extra mode that allows them operate non-USB applications. support those applications, ports pins (Port used only during event distinguish between non-USB applications. This documented datasheet section 8.1, illustrated schematic diagram Figure reviewed follows: Cable connector resistance small Ohms large Ohms typical applications. time constant must greater than LEDs must tied lowest resistance path VCC. must bypassed high-frequency noise (0.01 µF). entry point should bypassed high-frequency noise (C2). Port must pulled during initial voltage ramp, operation. must tied VSS. LEDs driven sinking current, require current limiting resistors (R5,6,7) 7C634XX/5XX Microcontrollers applications which require that unit into suspend upon POR, Port must pulled during (this mode shown Figure This precludes this from functioning driver, does destroy utility this pin. value pull-down resistor from Port convenient value from 470K Ohms.
Cypress Semiconductor Corporation
3901 North First Street
Jose
95134
408-943-2600 February 1998
CY634XX/5XX Keyboard Families: Power-On Reset Considerations
Figure
Cypress Semiconductor Corporation, 1998. information contained herein subject change without notice. Cypress Semiconductor Corporation assumes responsibility circuitry other than circuitry embodied Cypress Semiconductor product. does convey imply license under patent other rights. Cypress Semiconductor does authorize products critical components life-support systems where malfunction failure reasonably expected result significant injury user. inclusion Cypress Semiconductor products life-support systems application implies that manufacturer assumes risk such doing indemnifies Cypress Semiconductor against charges.

There important cases initial voltage considerations that system desig

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