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Sign In Register. Quick Links Categories Recent Discussions. Categories The 10k resistors are the simplest solution, but will affect bandwidth somewhat. A resistor divider using 1k and 2k2 resistors will give good bandwidth, but will interfere with any signals that have pull-ups. You could pull up Prop inputs to 3V3 with 2k2's or 4k7's or so and feed the 5V inputs via 1N's so the circuit-under-test can only pull-down - this has the advantage of working with any voltage from 3V3 up 24V PLCs perhaps?
And 1N's are cheap and fast. Phil Pilgrim PhiPi Posts: 22, Use 74LVC-series logic buffers on your inputs. They are fast, run from 3. It's LVC , rw. Here's the datasheet for the 74 LVC www. RDL Posts: 2, Download this from Texas Instruments Thanks for the Docs guys!
Is the book still available for fairly cheap? I really would rather have books most of the time. Publison Posts: 11, Ok so in reference to the 1. So for a 1. This means a propeller can only detect a 1. So I guess after this I get a bit confused The 74lvc doesnt shift any logic levels it just provides a buffer with v inputs and an out put of vcc.
So im probably totlly wrong but I would think the way to go about this is to set the vcc of the line driver to 1. The high output of the buffer will be whatever its Vcc is, and the low will be zero.
So if you set buffer Vcc to 1. If you're willing to call 1. But you could raise Vcc to 2. You could also switch-select the buffer Vcc, depending upon which logic family you're testing up to 3. I just looked at the NXP datasheet. I'm astonished at how poorly characterized the DC operating conditions are. I'd go with the TI part, just to be on the safe side, although the two are probably virtually identical.
I acually am using the Ti part in this case i have no idea why i was looking at the NXP sheet. The reason theve been sitting is becuase NXPs data sheets werent very helpful i couldnt really figure out some of the details maybe ill give the TI sheets a look see, as id really like to use them as a hardware counter for the bs2.
Hmm so i just gooked this board up to my logic analyzer and if i connect input 3 the two inputs before it show the same data!
So I figured out the sfix for this is to pull down the inputs, but i dont have any room to put pull downs on the inputs I do on the output that go to the propeller but pulling the outputs down doesnt seen to fix this problem, would pulling the inputs up work maybe?
This really sucks I didnt realize these chips would have so much cross talk on there pins!! You never want to leave a logic input floating if you can avoid it. In your case the "crosstalk" is simple capacitive coupling. Pull-ups will work just as well as pull-downs. Sign In or Register to comment.
74LVC244 Philips Semiconductors, 74LVC244 Datasheet - Page 4
U74LVC244 BUFFER/DRIVER. Datasheet pdf. Equivalent
Sign In Register. Quick Links Categories Recent Discussions. Categories The 10k resistors are the simplest solution, but will affect bandwidth somewhat.
74LVC244 – Octal buffer/line driver with 5-volt tolerant inputs/outputs 3-Statetitle
easyest way to use a prop based logic analyzer on a 5v system?