PIC18F2620 input high voltage only 2V..? - Electronic Circuits Projects Diagrams Free

MrNobody · 14th December 2007, 02:25 AM

Hi,
Refering to PIC18F2620 datasheet, section 26.3 on DC characteristics, it says that the input high voltage is only 2V for VDD between 4.5V and 5.5V.

BTW I am doing a project using PIC18F2620 and ENC28J60 and i was wondering, if the input high voltage is only 2V, then why would i still need additional CMOS chip to act as voltage level translator/shifter for ENC28J60's output pin SO, CLKOUT and INT. I mean, shouldn't the output voltage of 3.3V be sufficient to change the PIC pin from a LOW state to a HIGH state..?

Any thoughts..
Thanks..

mister_e · 14th December 2007, 02:32 AM

You shouldn't have any problem if the signal is greater than the one stated in the datasheet. But why not running the whole board @3.3V?

kchriste · 14th December 2007, 06:10 AM

Quote:

Originally Posted by MrNobody

I mean, shouldn't the output voltage of 3.3V be sufficient to change the PIC pin from a LOW state to a HIGH state..?

It depends on the pin. Some IOs are schmitt level inputs and others are TTL level. Some pins are TTL when in normal IO mode and are schmitt when in special function mode. ie: it'll work on PORTB which has TTL level inputs but may not work on PORTC which has schmitt inputs when configured for general purpose IO. Schmitt inputs trigger high at a max of 0.8Vdd or 4V when running with 5V supply.

MrNobody · 14th December 2007, 02:29 PM

mister_e:
I thought about that but i was afraid i might face some problems later when interface with other peripherals such as LCD display..

kchriste:
Oh yeah, those pins have schmitt level inputs.. Thanks for pointing that out..

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14th December 2007, 02:25 AM	(permalink)
MrNobody	PIC18F2620 input high voltage only 2V..? Hi, Refering to PIC18F2620 datasheet, section 26.3 on DC characteristics, it says that the input high voltage is only 2V for VDD between 4.5V and 5.5V. BTW I am doing a project using PIC18F2620 and ENC28J60 and i was wondering, if the input high voltage is only 2V, then why would i still need additional CMOS chip to act as voltage level translator/shifter for ENC28J60's output pin SO, CLKOUT and INT. I mean, shouldn't the output voltage of 3.3V be sufficient to change the PIC pin from a LOW state to a HIGH state..? Any thoughts.. Thanks..

14th December 2007, 02:32 AM	(permalink)
mister_e	You shouldn't have any problem if the signal is greater than the one stated in the datasheet. But why not running the whole board @3.3V? __________________ Steve

14th December 2007, 02:29 PM	(permalink)
MrNobody	mister_e: I thought about that but i was afraid i might face some problems later when interface with other peripherals such as LCD display.. kchriste: Oh yeah, those pins have schmitt level inputs.. Thanks for pointing that out..