Post by thread:[PICLIST] [pic] What's schmitt trigger input?

Hi, I use PIC16C74 and set the port D as input. But it behaves as output, eliminating all the input signals. The spec. says that they are schmitt trigger inputs. What are "schmitt trigger input"? How to make the port as a "regular" input? Thanks. Tony -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

On 21-Jan-02 Tony Pan wrote: > Hi, > > I use PIC16C74 and set the port D as input. But it behaves as output, > eliminating all the input signals. The spec. says that they are schmitt > trigger inputs. What are "schmitt trigger input"? Have a look at http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/schmitt.html They are useful for cleaning up noisy signals. > How to make the port as a "regular" input? I expect your problem is not with the schmitt trigger inputs but more likly a programming bug. I'm not familiar with the 16C74 so I can't comment. Peter ---------------------------------- E-Mail: Peter Onion <.....ponionKILLspam@spam@srd.bt.co.uk> Date: 21-Jan-02 Time: 16:39:02 This message was sent by XFMail ---------------------------------- -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestKILLspammitvma.mit.edu

On 21-Jan-02 Tony Pan wrote: > Thank you for the reply! > > Is TTL input the "regular" input that does not have the noise elimination > feature? Ok, here's a simple explanation.... The label "TTL input" is to do with the signal levels used to represent '0' and '1'. Look at the specs for Vil and Vih and you will see that it essentially means that voltages near 0v are '0's and voltages near +5v are '1's. There is a region between these levels where the input is undefined The label "schmitt trigger" can be applied to TLL and non-TTL compatible inputs. The definitions of '0' and '1' are similar for schmitt and non-schmitt TTL inputs, but the points at which the change from '0' to '1' (and '1' to '0') are different. For regular input the decision points for '0' to '1' and for '1' to '0' are the same. For a schmitt trigger the '0' to '1' decision happens at a higher voltage than the '1' to '0' decision. I hope this helps. > > Tony > > P.S. I did find a software bug. I accidentally set port D in parallel slave > port mode. I suspected as much but since I've not looked at that PIC I wasn't sure exactly what port D supported. Peter. -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam.....mitvma.mit.edu

Hi, be careful not to set TRISE.4 to 1 unless you want PSP mode! I know what I am speaking! Regards, Imre +-----------------------------------------------------------------------+ | The information transmitted is intended only for the person or entity | | to which it is addressed and may contain confidential and/or | | privileged material. Any review, retransmission, dissemination or | | other use of, or taking of any action in reliance upon, this | | information by persons or entities other than the intended recipient | | is prohibited. If you received this in error, please contact the | | sender and delete the material from any computer. | +-----------------------------------------------------------------------+ On Mon, 21 Jan 2002, Tony Pan wrote: {Quote hidden}> Hi, > > I use PIC16C74 and set the port D as input. But it behaves as output, > eliminating all the input signals. The spec. says that they are schmitt > trigger inputs. What are "schmitt trigger input"? How to make the port as a > "regular" input? > > Thanks. > > Tony > > -- > http://www.piclist.com hint: To leave the PICList > EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads