| Electronics > Beginners |
| Best way to drive a 5V TTL line with a 3v3 GPIO? |
| << < (3/6) > >> |
| nockieboy:
--- Quote from: Hero999 on December 17, 2018, 12:49:33 pm ---There are open collector HCT ICs available, such as the 74HCT05, but it doesn't need to be open collector. Shorting the internal pull-up resistor to +5V will do no harm. http://www.sycelectronica.com/semiconductores/74HCT05.pdf --- End quote --- Oh okay, that sounds like a much better option then as I don't want to have to add another chip if I don't have to - I can just use the existing 74HCT04? Actually, thinking about it, I use the 04 to drive power LEDs so yes, I guess it should be fine. :-+ |
| emece67:
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| mikeselectricstuff:
--- Quote from: emece67 on December 17, 2018, 02:26:49 pm ---Why not using an integrated solution? This worked well for me http://www.ti.com/lit/ds/symlink/txb0108.pdf. Regards. --- End quote --- Those bidirectional shifters are pure evil unless you really need bidirectional translation. Doesn't take much capacitance to make them oscillate |
| nockieboy:
--- Quote from: emece67 on December 17, 2018, 02:26:49 pm ---Why not using an integrated solution? This worked well for me http://www.ti.com/lit/ds/symlink/txb0108.pdf. Regards. --- End quote --- I've actually got a TXB0104D in the design doing level translation for the SPI bus from the ESP32 to a couple of MCP23S17s, but I didn't fancy trying to squeeze another chip onto the board, especially if I can make it work using unused inverters on an HCT04 I've got in the system already. The MCPs are connected to the Z80's address, data and control buses (which are 5V), hence the voltage translation as the MCPs are also powered by the 5V supply. --- Quote from: mikeselectricstuff on December 17, 2018, 03:18:26 pm ---Those bidirectional shifters are pure evil unless you really need bidirectional translation. Doesn't take much capacitance to make them oscillate --- End quote --- Oh? I've never used them before... in fact, the whole design for the ESP32/Z80 interface exists only in DipTrace at this moment in time, or as a high-level graphical representation to give the idea of how it should all fit together.. I was planning on making another post - probably in the Projects section of the forums - asking for feedback on that design and confirmation that it'll theoretically work before I start trying to prototype it. |
| mrpackethead:
--- Quote from: nockieboy on December 17, 2018, 12:08:53 pm ---Would the 74LVC4245 be able to do the same? I have 3 free pins on one of those chips - if they are able to pull the 5V lines low, I could use the remaining pins. --- End quote --- There are some LVC Parts that do level translation, such as the 4245, ( its got dual power supplies ), but as a general rule you cant'. most HCT parts (all?) can take a 3.3V input when its on 5V supply ), and get 5V level outputs. |
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