[ad_1]
By now, 3.3V has turn into a cushty and customary logic degree for principally something you could be hacking. Nonetheless, typically, you continue to have to interface your GPIOs with gadgets which might be 5 V, 1.8 V, or one thing even much less frequent like 2.5 V. At this level, you would possibly come upon autosensing degree shifters, just like the TXB010x sequence Texas Devices produces, and resolve that they’re good — no want to fret about pin course or trouble with pullups. Simply wire up your GPIOs and the 2 voltage rails you’re good to go. [Joshua0] warns us, nevertheless, that not every little thing is hunky dory within the automagic shifting world.
Throughout board bring-up and multimeter probing, he discovered that the 1.8 V-shifted RESET sign went right down to 1.0V — and its 3.3 V counterpart stayed at 2.6V. Was it a present struggle between GPIOs? A defective connection? Voltage rail instability? It received extra complicated because the debugging session uncovered the shifting working usually as quickly because the take a look at factors concerned have been probed with the multimeter in a sure order. After re-reading the datasheet and recognizing a be aware about reflection sensitivity, [Joshua0] realized he ought to attempt to probe the alerts with a high-speed logic analyzer as a substitute.
At a excessive sufficient frequency, he’s discovered the alerts always oscillating forwards and backwards, because the shifter’s autosensing mechanism was being fooled into switching by the sign reflections at a quick sufficient fee to confuse the multimeter into studying the alerts as being at an in-between voltage. It seems that even with alerts that are supposed to change solely as soon as in a board’s bootup, these shifters would possibly offer you extra bother than they’re value. To not fear, nevertheless, as you continue to have myriad methods to degree shift any sign you need.
[ad_2]
Supply hyperlink
