Community. An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications. 74HCTD, Nexperia Buffers & Line Drivers OCTAL BUFFER 3-STATE datasheet, inventory, & pricing. 74HC; 74HCT Octal buffer/line driver; 3-state. Rev. 03 — 22 December Product data sheet. Table 1: Quick reference data. GND = 0 V; Tamb =
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74HC244; 74HCT244 Octal Buffer, Line Driver; 3-state
So far I have just ignored this, and most of the time it works, but I would like to avoid the ‘unsafe’ feeling it gives me. HC, or look for some datashest schmitt-trigger.
Then you could buffer the dtaasheet up. Normally for input I connect direct or with a resistor divider. For output direct connection without problems. You might choose the 74HCT — that would give you 8 lines in a single package. And it’s available in an easy-to-use through-hole package. Going the other direction, you may not need a translator — some mbed pins are 5-volt tolerant.
Check the data sheet for the LPC If your external devices are of 74HC or 74LS series, you can connect them safely and they will work reliably. You can look at the data sheets how the logic high voltage is defined should be either 2 volts, 0. I have used the 74HC as logic converter, which worked flawlessly. I haven’t seen any logic level converter in DIP packages.
dataeheet Actually, it’s just the opposite. So a 74 HCT is indeed the proper choice. As Hendrik has found, it happens that HC parts also work much of the time, since at room temperature their “typical” spec for VIH actually falls below their guaranteed “minimum” spec of 3.
See Table 7 on page 6 of this data sheetunder “V IH “. But I dataeheet rely on “typical” values if you want a robust design.
I just stumbled upon this thread again and got really embarrassed for not giving proper feedback. I tried several HCT buffer type parts and all of them worked! A digital xatasheet can drive 40mA, up to a total of mA. While inputs are 5V tolerant, outputs are not. Also, the 40mA figure quoted in the handbook for output drive is related to the short circuit limits.
Normal logic-level output current is lower.
The LPC data sheet explains this in more detail. Most 74HCT parts when run on 5V require 3.
Given that the LPC, and much other 3. However the mopst popular device in my arsenal, which will translate both ways, from a variety of voltages to a variety of voltages is the 74hcr244d In my opinion the 74HCT “trick” 74jct244d really a trick, the voltage levels are right because the parts are designed that way. The problem is that generally you can detect a pin going to or from tristate OR transmit to the pin, but not both.
74HCTD Datasheet PDF – Philips Electronics
As a result magic translators tend to have limited drive or are open-drain with a pull up. In comparison a normal logic gate has well known logic levels and full drive capability so you won’t get tripped up by pull-up resistors or loading. I notice that the 74LVC8T mentioned above has a direction 74hc244d, and does not rely on auto-sensing.
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Please, contact us at support mbed. As most of my peripheral circuits run on 5V, I need some way of level shifting. I’ve seen discrete versions of bidirectional level translators consisting of just one FET. I’d prefer a chip with lines, not necessarily bidirectional. What do you use? But I attribute this to lack of coffee – I should have verified my claims: Sorry for the confusion. Thanks all, dahasheet an added cheer for Hexley dominating the mbed challenge! Going to try some simple pullup resistors.
Table 7 on page 45 gives the following limits for standard port pins: There is one dirty trick that many of us use. Run HCT parts on 5V and directly drive the inputs from 3.