Post by thread:[PIC:] are Inputs/Output pins 3.3 volt compatible

Greetings: I need to connect the input/output pins of a 3.3 volt device to a PIC 18F452. It looks - from reading the manuals (DS39564B Par22.2 and DS39533 Par32.6) - like the I/O pins on the PIC can handle the 3.3 volt level with no problems. That is, it appears that LOW is anything below 0.8 volts and HIGH is anything above 2.0 volts, but the way the spec is written it is anything but clear. Is anyone doing this successfully WITHOUT a level shifter chip? I want this to be a Q&D test of applicability, and I don't want to hack the PCB to add level shifting if I don't have to. Roy J. Gromlich -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

>I need to connect the input/output pins of a 3.3 volt device to a PIC >18F452. It looks - from reading the manuals (DS39564B Par22.2 and DS39533 >Par32.6) - like the I/O pins on the PIC can handle the 3.3 volt level with >no problems. That is, it appears that LOW is anything below 0.8 volts and >HIGH is anything above 2.0 volts, but the way the spec is written it is >anything but clear. Is anyone doing this successfully WITHOUT a level >shifter chip? I want this to be a Q&D test of applicability, and I don't >want to hack the PCB to add level shifting if I don't have to. Be aware that having a PIC input at 3.3V when the PIC is operated at 5V MAY cause the PIC to consume more current than normal. Probably will. BUT that is not to say that the current consumption will be outrageous; I just (see the "Current Hog" thread) found that having a pin at 3V on a 3.3V PIC caused the circuit to draw 3.5 mA rather than .5 mA with the pin setup as an analog input. What sort of device are you interfacing? For example, Atmel's DataFlash chips have "5-volt tolerant" inputs, and others may too. Or, can you use an 18LF452 and run the PIC at 3.3V as well? Mike H. _________________________________________________________________ FREE pop-up blocking with the new MSN Toolbar get it now! http://toolbar.msn.click-url.com/go/onm00200415ave/direct/01/ -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

Right you are - I hadn't given that a lot of thought. OK - running the PIC at 3.3v would be nice for several reasons, but its a no-go. I need the 5 volt swing to control off-board stuff which is not mine to modify. This is customer equipment and we ake it as we find it. Anyway, I have a MAX232 connected to the Rx & Tx lines for the main serial I/O, and a few MAX3100 UART chips for secondary I/O, in addition to the A/D inputs and 8 bits of CMOS I/O. That all works just fine. I want to pull the MAX232 out of its socket (this is for testing, not production) and connect the Rx & Tx pins to a Lantronix Xport module, which will put this handy dandy little protocol converter card on the internet. If you haven't seen it, take a look at the Lantronix Xport device - a full tcp/ip stack and simple web server in a slightly elongated RJ45 jack! Amazing. So I guess I will put a few resistors and such on the adapter board to hanlde level shifting. Like I said, this is for evaluation only - in a production unit it would be taken care of properly. Thanks, Roy -- Original Message -- From: Mike Hord <gaidinmdKILLspamHOTMAIL.COM> To: .....PICLISTKILLspam.....MITVMA.MIT.EDU Send: 2004-05-20 Subject: Re: [PIC:] are Inputs/Output pins 3.3 volt compatible ??? >I need to connect the input/output pins of a 3.3 volt device to a PIC >18F452. It looks - from reading the manuals (DS39564B Par22.2 and DS39533 >Par32.6) - like the I/O pins on the PIC can handle the 3.3 volt level with >no problems. That is, it appears that LOW is anything below 0.8 volts and >HIGH is anything above 2.0 volts, but the way the spec is written it is >anything but clear. Is anyone doing this successfully WITHOUT a level >shifter chip? I want this to be a Q&D test of applicability, and I don't >want to hack the PCB to add level shifting if I don't have to. Be aware that having a PIC input at 3.3V when the PIC is operated at 5V MAY cause the PIC to consume more current than normal. Probably will. BUT that is not to say that the current consumption will be outrageous; I just (see the "Current Hog" thread) found that having a pin at 3V on a 3.3V PIC caused the circuit to draw 3.5 mA rather than .5 mA with the pin setup as an analog input. What sort of device are you interfacing? For example, Atmel's DataFlash chips have "5-volt tolerant" inputs, and others may too. Or, can you use an 18LF452 and run the PIC at 3.3V as well? Mike H. _________________________________________________________________ FREE pop-up blocking with the new MSN Toolbar get it now! http://toolbar.msn.click-url.com/go/onm00200415ave/direct/01/ -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestspam_OUTmitvma.mit.edu