The other nice thing about the TI Link protocol is the slower device sets t= he transfer rate, there is no dealing with baud rate differences due to osc= illator speeds etc., so it is an ideal way of communicating between two dev= ices using internal oscillators that may have mismatched frequencies due to= temperature drifts and so on. > -----Original Message----- > From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf > Of John Gardner > Sent: 17 May 2017 20:54 > To: Microcontroller discussion list - Public. > Subject: Re: [EE] Low-cost differential signaling >=20 > I should have added that the hardware is superfluous with a PIC, >=20 > but it helps to understand what's going on. Totally bit-bangable, >=20 > even by me... :) >=20 > On 5/17/17, John Gardner wrote: > > Check this out... > > > > http://merthsoft.com/linkguide/hardware.html > > > > On 5/17/17, Harrison Cooper wrote: > >> Neil > >> > >> I had a similar application, where the two PICs would communicate > >> over a bit of a distance. Undefined, but really up to 20 or 30 feet > >> depending on how the end user ran the cable. In my case, cost was > >> not as much of an issue as reliability as I did not want a call > >> saying...we are not seeing the data all the time. > >> > >> I did two things to try and minimize interference and try and obtain > >> decent signal integrity, and that was to use CAT5 (cables are > >> cheap...monoprice) and ran the signals at 12V. Mine was only slave > >> transmit to host receive, thus I used a driver that ran it basically > >> rail to rail, and then opto couplers at the other side. Systems have > >> been in place for over 4 years..maybe 5, and never had an issue with > >> data loss. If your counting pennies, then maybe its too expensive, > >> but these were low run rate systems. > >> The reason I went with 12V is that it was available, and since the > >> cables were an unknown, I could also afford the IR drop along the way. > >> > >> -----Original Message----- > >> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On > >> Behalf Of Neil > >> Sent: Wednesday, May 17, 2017 1:08 PM > >> To: Microcontroller discussion list - Public. > >> Subject: [EE] Low-cost differential signaling > >> > >> I'm doing one-way digital communications between 2 PICs about 12 feet > >> apart. > >> ~50 kHz max. Cable currently has 12V, ground, and one data wire > >> (5V direct from a PIC 18F output). Nothing is twisted yet -- just > >> straight wires. At this stage, it's functional and works fine as it > >> is, but I'd like to add EMI/noise immunity (against possible external > >> noise from other nearby signals). Shielding is noticeably increasing > >> that cabling cost, so I'm thinking of differential signaling instead. > >> Looking for a simple way to do this. > >> > >> First thought was to use RS-485 or similar differential transceivers, > >> but that adds a few dollars, which is higher than I'd like. CAN > >> transceivers are lower cost (~$0.40 each side). However, CAN is a > >> relatively low-level signal, so I'm thinking that I can just use 2 > >> I/O pins on the sender to create my own differential 5V-ish signal, > >> and use the comparator on the receiving PIC to process the > >> differential signal. > >> I would need to add some resistors at the receiving end as the > >> (PIC32) comparator inputs can only handle up to 3.3V on that side. > >> From anyone's experience, would this even make a dent in the system's > >> ability to reduce noise effects? Additionally, I am hoping to have > >> the sender be open-drain, and pull-up at the receiver. Should this > >> be hard-driven to 5V instead for better noise immunity? > >> > >> Another thought is that I have 12V available at the sender, so I can > >> use that for the signaling level, but that adds a couple transistors. > >> Or I can stay open-drain at the sender and pull up to 12V at the > >> receiver, then voltage divide. Would it make a difference for > >> differential signaling? > >> > >> Thanks, > >> -Neil. > >> > >> -- > >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > >> View/change your membership options at > >> http://mailman.mit.edu/mailman/listinfo/piclist > >> Western Digital Corporation (and its subsidiaries) E-mail > >> Confidentiality Notice & Disclaimer: > >> > >> This e-mail and any files transmitted with it may contain > >> confidential or legally privileged information of WDC and/or its > >> affiliates, and are intended solely for the use of the individual or > >> entity to which they are addressed. If you are not the intended > >> recipient, any disclosure, copying, distribution or any action taken > >> or omitted to be taken in reliance on it, is prohibited. If you have > >> received this e-mail in error, please notify the sender immediately > >> and delete the e-mail in its entirety from your system. > >> > >> > >> -- > >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > >> View/change your membership options at > >> http://mailman.mit.edu/mailman/listinfo/piclist > >> > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .