How to properly connect to a small flash rom chip without desoldering? - Page 1
Forum section: electronics / beginners

author: markusz
author_rank: Contributor
timestamp: January 31, 2022, 02:47:35 am
content: Hi experts,I'm preparing to dump a flash rom in my router with a Tiva TM4C123G launchpad. Please see the attached photo for the rom chip. It's approximately 5mm x 5mm so the pins are pretty small.I believe it's a Gigadevice GD25Q32C chip (probably Package SOP8 208MIL) and also attached its datasheet. I have a few constraints:I must use Tiva launchpadI cannot use any rom programmer or other breakout board, so everything goes from Tiva to rom (It has SSI so I think it can interface with SPI chips)I cannot remove the chip from the PCBAfter some research I figured there are two ways to connect the rom chip to the launchpad:- Method 1: Purchase some alligator clips to Dupont jumper wire (male head). I would connect the alligator clips to six pins of the rom chip for READING ONLY, and the female heads to Tiva launchpad. So the connection looks like this: CS->some pin, SO->some pin for reading data, WP->some pin for removing write protection, VSS->ground, VCC->3.3V output, SCLK to some pin- Method 2: Purchase a SOIC8 test clip and use the same connections (probably through male-female head) as above.I'm ordering both but there are going to be some weeks for them to arrive. My questions are:- For method 1, would alligator clips be too large for this chip?- For method 2, I consulted multiple tutorials (they all use some Adruino board) and looks like the end of the SOIC8 test clip always connect to a small PCB, as shown here:Do you know what it is? *Edit*: I looked at Amazon and it looks like a convertor, but what's the purpose of it?

author: Manul
author_rank: Super Contributor
timestamp: January 31, 2022, 03:25:16 am
content: I don't know about the connections, but are you sure it is a good idea to read it in circuit? You will basically power whole 3.3V rail externally, which might be an issue by itself and also how you avoid possible collision with the router SPI bus? Even if the bus is idle, CS, CLK and MOSI could be driven by the router (low-z). Generally such idea is not very good.

author: markusz
author_rank: Contributor
timestamp: January 31, 2022, 03:45:06 am
content: Quote from: Manul on January 31, 2022, 03:25:16 amHi Manul sorry I'm a beginner in this. Did you mean that if I power the chip from the launchpad, the 3.3V might "wake" other chips along the way? I don't now if other chips are low-resistant, but my previous thought was, if I turned the router off and power 3.3V from outside, should be OK?Essentially I'm trying to follow the tutorial here, however it's a completely different device so I'm driving blindly.https://blog.nvisium.com/intro-to-hardware-hacking-dumping-your-first-firmware

author: markusz
author_rank: Contributor
timestamp: January 31, 2022, 03:49:34 am
content: Quote from: Manul on January 31, 2022, 03:25:16 amBTW, in additional to what I replied, I also found four "holes" on the PCB, this is probably JTAG but sadly I don't have soldering equipment. Plus I prefer not to boot the device up.

author: Manul
author_rank: Super Contributor
timestamp: January 31, 2022, 10:05:26 pm
content: Quote from: markusz on January 31, 2022, 03:45:06 amYep, something like that. Flash chip needs to be powered. So two options:1. You power the router anddon'tconnect power externally2. You keep router off and connect power externallyPowering externally will of course power everything what is on the same power rail (and child rails). Could be most of the router hardware. Now one knows without looking.Anyway, the problem is that there might be SPI bus collision. For example, router hardware will pull SPI clock LOW while your externally connected device will try to pull HIGH. You get the idea.So options are these:1. Remove the IC and read without any constraints.2. Pull the reset line of the router so SPI bus is not driven by router (high-z), but first you need to find the reset line and do modification.3. Just proceed like you don't care and hope that it will work.Maybe you are lucky and you will find that SPI bus is idle and in high-z. But I would check that before attemting to drive these digital lines.Also you might be able to get the flash image file without dumping it - from manufacturer's firmware update package.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 01, 2022, 11:33:52 am
content: Very unlikely to get lucky; even if the CPU is idle, it still likely drives the MOSI, CLK, nCS lines.Just desolder it. You are already lucky because the flash is in such huge, easy to handle, low pin count package. Desolder it, place it on a temperature resistant surface and solder wires. Do the reading magic. Then clean the original footprint from excess solder and flux residue (so that end result will look better), and solder the chip back.You can always practice desoldering and resoldering on any dummy PCB with similar packages. This is time well spent.