[cctalk] Re: RP2350 5V Input Tollerant Pins

You and the referenced thread are quite correct that the RP2050 is a curate's egg : the 5V tollerance being conditional on Vddio at 3v3. Some real translators do not have this limitation, eg 74LVC. However, some do, eg 74LV1T is only "good" unpowered to 4v5 input (GEfGW ?). The RP2050 lacks the note which TI commonly append that going overvoltage on an (unpowered) pin is OK iff the current limits are observed. Whether this trade is available on the RP2050 is an interesting question. A common aproach is to fit series resistors as crude current limiters, 100R 1k 10k say. I shall observe that this thread neatly illustrates how building test instrumentation out of inexpensive components is not so easy, and that emanuel stiebler's observation that a good nights rest is best assured by using "real" voltage translators has merit. And, as you observe the reason for discussing the RP2050 and these issues here is the construction of adjuncts to old hardware. In new hardware you would have power sequencing and reset nets to control the low voltage to higher voltage power sequencing, reset release and shutdown arrangements. Martin -----Original Message----- From: Jay Logue via cctalk [mailto:cctalk@classiccmp.org] Sent: 30 July 2025 22:59 To: cctalk(a)classiccmp.org Cc: Jay Logue &lt;jay-cctalk0092(a)toaster.com&gt; Subject: [cctalk] Re: RP2350 5V Input Tollerant Pins I have not studied the RP2350 datasheet closely (and I'm definitely not an EE), but as I understand it, the caveat here is that 5V tolerance only exists while the device is fully powered (IOVDD at 3V3).  At lower supply voltages (e.g. during startup), digital I/O pins may be damaged by voltages higher than 3.3. The topic is discussed in more depth here, and in linked threads: https://forums.raspberrypi.com/viewtopic.php?t=375118 To bring this somewhat back around to cctalk, I faced this issue when designing my console adapter for the PDP-11/05 (github <https://github.com/jaylogue/pdp1105-console-adapter-v2>). It is based on the  rPI Pico (RP2040), which has a similar limitation.  I wanted the device to be able to be powered from the 11/05 itself.  But at power on, the supply voltage races with the SERIAL OUT (TTL) line, and always looses due to the time it takes for the onboard 3V3 regulator to stabilize.  Since I cared more about simplicity than power efficiency or speed, I went with a simple voltage divider rather than a level shifter. --Jay On 7/30/25 07:04, Martin Bishop via cctalk wrote: