With an atmel microcontroller when you write 1 to a pin does the pin actually read +5, or is that only when you have an internal pullup on that pin? Thanks Colin
Quick Microcontroller question
Aug 26, 2005
3 Replies
Colin wrote this in :
It reads +5 when high. But be aware that most atmels can sink more current than they can source.
MVH,
Vidar
www.bitsex.net
It will be a "logic 1" but the guaranteed minimum voltage is 4.2 V. Check the datasheets; there is some variation among the AVR family in this parameter. Even with pull-ups, the actual value may be less than
5.00 V if you're sourcing current.
Rich Webb Norfolk, VA
On the 8051 equivalents (89C52, etc.) one port is open collector, so requires an external pull-up, if I recall correctly.
Read The Fascinating Manual for the particular microcontroller you are using to be sure....
Peter Bennett, VE7CEI
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