Method to switch between two IC's - Page 1
Forum section: electronics / beginners

author: leham
author_rank: Regular Contributor
timestamp: August 21, 2014, 01:27:45 am
content: Hi guys/gurlsI have a simple question, but it seems I'm too simple to work out the answer.I have Two IC's here, identical pin out just different code.I want to be able two switch between the two, each IC has 28 pins, I could take it down a bit and tie all the grounds together(?).What would be a cheap method in doing so? My end goal is to be able to select either IC using one switch, would a whole bunch of solid state relays work??Sorry for the noob questionThanks in advance!EDIT:I should also add that these ICs are surface mount, so I plan on getting a Pcb made, having said that the smaller my overall project the better..

author: Artraze
author_rank: Contributor
timestamp: August 21, 2014, 02:38:56 am
content: Since you say "just different code", would I be correct in assuming that the ICs you want to swap out are microcontrollers?If that is the case, then why not simply program both functions onto a single microcontroller? You could select between functionality using a I/O pin.Another possibility is if your ICs have a reset pin, you could hold one IC in reset and let the other run. It would require looking over the datasheet in detail, of course, but most of the time when an IC is in reset state the input pins are ignored and the output pins are high impedance (and so not outputting anything). In this case you could just hard wire the chips directly together.Does that help? If not, perhaps you could explain the problem you're facing that you wish to solve by switching ICs?

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 21, 2014, 04:22:06 am
content: A great deal depends on WHAT the chips are.For example, if they are some type of chip with a "select" or "enable", that would be an ideal solution.If they are microcontrollers, you might be able to write code into them to disable all the I/O pins on the disabled chip, etc.But there are dozens of caveats and potential show-stoppers depending on exactly what knid of chip it is.Your question is almost impossible to answer without knowing the identity of the chips you are talking about.It seems extraordinarily unlikely that a bunch of SSRs or switches would be a viable solution.

author: Whales
author_rank: Super Contributor
timestamp: August 21, 2014, 05:02:00 am
content: I would build both chips onto two daughter-boards. Connect these to the main PCB by ordinary headers.

author: Kjelt
author_rank: Super Contributor
timestamp: August 21, 2014, 07:24:26 am
content: If they are microcontrollers AND the reset state of the microcontroller is all I/O pins floating AND each microcontroller has its own (internal?) clocksource then you can piggyback both ic's and switch between the two using a switch on the reset lines of the microcontroller, so keep one of them in continuous reset.For safety power down the board before switching just to be on the safe side.This needs a lot of checking though

author: leham
author_rank: Regular Contributor
timestamp: August 21, 2014, 12:39:53 pm
content: They are two pif lockout IC's used in the nintendo 64, I don't think they have a reset pin and I can't program them.Thanks for all the help guys

author: leham
author_rank: Regular Contributor
timestamp: August 22, 2014, 10:33:04 pm
content: Here is the pin out for the pif.I will also need to switch between two crystals, one for each pif.

author: leham
author_rank: Regular Contributor
timestamp: August 22, 2014, 10:37:59 pm
content: These two where never intended to be on the same (bus?) so they don't have a C/E pin, is there some other ic that can be used to switch multiple separate lines at once ?I tried googling but didn't know what to look for..I have no problem soldering, I'm just still learning about integrated circuits and the like, so excuse my ignorance.Thanks

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 22, 2014, 11:42:34 pm
content: That "enable_high" pin 8 looks like a prime candidate!If you had two identical chips (except for the contents, of course), and you wired them together, pin-for pin, EXCEPT pin 8.You could wire each pin 8 to a resistor (like 1K ohm) up to the VCC power voltage.Then you alternately take either pin 4 and short it to ground, presumably with your toggle switch.Whichever chip has pin 8 = high is enabled, and the other chip (pin 8 = low) is disabled.Without some kind of diagram or something, your crystal question is anybody's guess.Do you know where the crystal connects to the chip? Is it pin 9? Where does the other side of the crystal go?

author: leham
author_rank: Regular Contributor
timestamp: August 23, 2014, 12:16:12 am
content: Really, will it be that easy?! Wow I don't know why no one has thought of that. People have tried just swapping vcc and a few other pins but it would cause interference.As far as the cyristal goes I was just going to switch it separate, maybe use a dtdp switch.What do you think?

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 23, 2014, 12:49:04 am
content: Of course we don't know what a "pif chip" is. If we actually knew what the chip is and could examine the data sheet we would know for sure.But on most NORMAL chips, the "enable" pin does just that--it ENABLEs the chip. With that pin low (grounded) is DISABLES the chip.I am guessing that the "enable" pin works the same on this unknown "pif chip". Do we even know what "PIF" means?Depending on the wiring of the crystal (which I asked about but you did not respond), it may be sensitive to stray capacitance.So it may be a problem to run long wires out to a switch from the crystal circuit.Of course if this mystery "PIF" chip works like normal chips, you may not have to switch the crystal at all.FULL DISCLOSURE: Since we don't know what this "PIF chip" is, we don't really know whether the "enable" pin works like it does for normal chips.Even if the enable pin works as expected, we also don't know whether it is safe to wire all the pins together. Again, because we don't know what this "PIF chip" is.If those chips are easy to replace, I might consider just trying it. However if those chips are rare and/or irreproducable, I probably wouldn't try this.NOT RECOMMENDED unless you can get better information about the chips, ideally, the full manufacturer's data sheet.

author: leham
author_rank: Regular Contributor
timestamp: August 23, 2014, 01:24:14 am
content: Clam down, the chip is proprietary ic made by sharp for nintendo. There is no data sheet for it.. The best I could find was that image..I thought this was a friendly forum...Anyway, all I really want to do is just switch all the pins from either ic..I have seen people use two 4066'shttp://nfggames.com/forum2/index.php?topic=2531.0Sorry I'm not perfect..

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 23, 2014, 12:03:15 pm
content: Sorry, I was not trying to attack you or put you down. I just don't know how rare or available these chips are.I was trying to warn you about the potential harm depending on things we apparently don't know about the chips.Any kind of experimentation in uncharted territory has risks, and I just don't want you to blow up some rare component.There are laboratory experiments that could be used to determine if the enable pin really disables all the pins so that the chip can be paralleled with another one. But we don't know if you are equipped to do this kind of experiment. Or what the consequences of failure would be.

author: leham
author_rank: Regular Contributor
timestamp: August 24, 2014, 01:38:49 am
content: That's okI don't have the right tools to checkWhat ever method I end up with, I will want to make a PCB and have it made by dirty Pcb or some other company, this is really only going to be for one system.So I take it a bunch of ssr's would be out of the question?Could you take a look at that link, would a few of those 4066 ic work. Obviously If I am going to swap 25 connections I'll need a few more than him?Thanks

author: Bukurat
author_rank: Regular Contributor
timestamp: August 24, 2014, 02:27:43 am
content: Being an inquisitive type, I googled "Nintendo PIF".It appears to be some sort of Challenge - Response protection circuit.http://www.emutalk.net/threads/53217-N64-PIF-CIC-NUS-6105-Algorithm-Finally-ReversedDave once pulled one to bits.https://www.eevblog.com/forum/blog/eevblog-491-nintendo-64-game-console-teardown/Some good photos there.

author: Zero999
author_rank: Super Contributor
timestamp: August 24, 2014, 01:32:12 pm
content: Quote from: leham on August 24, 2014, 01:38:49 amOr use an analogue multiplexer with more channels such as the 74HC4053.http://www.nxp.com/documents/data_sheet/74HC_HCT4053.pdf

author: leham
author_rank: Regular Contributor
timestamp: December 31, 2014, 04:07:49 am
content: Hmm ok,There has been someone who has managed to do what I'm looking to do but they only sell completed pcbs with all the IC's shaved :/Two are going to be the custom chips form two systems..I'll try to find the photosThe two larger chips look to be the custom chips I'm talking about, one will be from a PAL unit and the other a NTSC unit.This circuit is apparently automatic in selecting the correct chip (pal or NTSC) I just don't know how..I'm not really interested in that feature, I'm just wondering if there is a way to select either using a single switch..I'm only new to playing with ICs sorry. I don't think these IC's have any simple /CE pinThanks guys

author: pmbrunelle
author_rank: Regular Contributor
timestamp: December 31, 2014, 05:11:12 am
content: Why use solid-state relays when you can use mechanical relays?You can get fairly compact DPDT signal relays intended for telecom usage, even in surface-mount form factor if you like.14x DPDT relays, done.

author: leham
author_rank: Regular Contributor
timestamp: January 01, 2015, 12:06:44 am
content: Cool ideahaha I tend to over think things hahaDo you have a link to some?12v or 5v doesn't really matter as this system has both rails..

author: dannyf
author_rank: Super Contributor
timestamp: January 01, 2015, 12:10:52 am
content: Why not just use switches? Set a pin to use one chip and clear it to use another. At most 28 switches.Another "nasty" approach is to flow the ground pin(s) to take out a chip not used.