Author Topic: CH341A Serial Memory Programmer Power Supply Fix  (Read 730415 times)

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Offline md5001996

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #100 on: August 24, 2024, 02:00:38 am »
My modification of the black programmer. It can be switched from 5V to 3.3V and from 3.3V to 5V. For 1.8V chips I use a simple adapter.

See my pics... i cant solder as says in your photos...
 

Offline Tantratron

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #101 on: November 15, 2024, 09:05:30 am »
All Vcc connections in the ZIF socket are 3.3V but the CH341A is powered at 5V.
So all I2C and SPI signals are 5V while the external memory is powered at 3.3V.
There are no limiting series resistors on those signals.

One simple solution to fix this issue is to simply bypass the 1117-3.3V regulator.
I can use the hot air station to remove the 1117 and then short-circuit the input with the output.

My question is, is it safe to just do the short-circuit without removing the 1117 linear regulator?

Hi,

The trick is, that you miss 2nd LDO, that is inside CH341A chip.
Check datasheet.

At end of chapter 5.2 硬件说明 (Hardware description) is stated:
CH341芯片支持5V电源电压或者3.3V 电源电压。当使用5V 工作电压时,CH341 芯片的VCC 引脚 输入外部5V 电源,并且V3 引脚应该外接容量为0.01uF~0.1uF 的电源退耦电容。当使用3.3V 工作
电压时,CH341 芯片的V3引脚应该与VCC引脚相连接,同时输入外部的3.3V电源,并且与CH341芯
片相连接的其它电路的工作电压不能超过3.3V。
It can be translated:
The CH341 chip supports a 5V supply voltage or a 3.3V supply voltage. When using a 5V supply voltage, the VCC pin of the CH341 chip inputs an external 5V power supply, and the V3 pin should be externally connected with a power supply decoupling capacitor of 0.01uF to 0.1uF. When working with 3.3V voltage, the V3 pin of the CH341 chip should be connected to the VCC pin, and an external 3.3V power supply is input, and the CH341 core is connected.
The operating voltage of other circuits connected to the chip cannot exceed 3.3V.

As far as I understand, that mean, that chip have internal 3.3V regulator and IO pins are NOT 5V tolerant. It mean, it always use 3V3 for communication with eeprom.

Hello, I've purchased this week from Amazon this model https://www.amazon.fr/gp/product/B07SNTL5V6 but I would need some confirmation or help regarding if the 5V issue is solved nowadays.

Attached 2 pictures of the programmer, I've only connected to my USB port from my iMac then used my DDM to check the 8 pins corresponding to target SPI NOR chip (25D40 so 3.3V). I have not yet connected the SPI NOR memory to avoid any frying so the voltage values read from the CH431A connector are not loaded. It seems that Vcc (pin 8) Hold (pin 7) Write Protect (pin 3) do show 3.3V but how about the 4 pins (Chip Select, MISO, MOSI and CLK) which show 5V ?

The jumper supposed to select 3.3V is shown in the pciture but does this model will self-shift to 3.3V on all pins, why some pins are 5V and other 3.3V ?

Thank you in advance, Albert
 

Offline Ian.M

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #102 on: November 15, 2024, 02:15:12 pm »
A CH341A chip with no additional dual supply level shifters cant "self-shift to 3.3V" when a serial EEPROM or FLASH memory is connected.
What is actually happening is the  memory is dragging down the signal voltages, and possibly dragging its Vcc supply above 3.3V, via the memory's input clamping diodes.  As David said back in reply #81
You're forcing the pins to clamp the voltage coming from the ch341, it's up to you to "freak out" or take the risk.
But one day you might want to read some important memory and get a surprise.

You have the same issue the O.P. did when he started the topic, and you need to do the mod to work safely with 3.3V memory chips - either the permanent 3.3V mod or the switchable version if you also need 5V capability.
 

Offline flachyjoe

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #103 on: November 16, 2024, 10:48:19 am »
Hi !

I've buy this one https://www.ebay.fr/itm/324505422583 I've received a black card labelled "CH341 Pro" on front side and "CH341 MinProgramment" on back. No "a" !? and no version number.

The top pin row is marked "1 2 3 TX RX GND 3.3V" when I see "1 2 3 TX RX GND 5V" on the previous posted picture. Could it be a fixed design ?
 

Offline Tantratron

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #104 on: November 16, 2024, 11:12:34 am »
Bonjour flachyjoe,

Ther seems to be a slight difference between CH341 and CH341A, look this here which part of is translated in french

En mode port d'imprimante, le CH341 fournit un port d'imprimante USB standard qui combine le protocole USB et le système d'exploitation Windows utilisé pour mettre à niveau une imprimante parallèle ordinaire directement vers le bus USB. En mode parallèle, le CH341 fournit un parallèle 8 bits en mode EPP ou MEM. Il peut être utilisé pour entrer/sortir des données directement sans MCU/DSP. En outre, le CH341A prend également en charge certaines interfaces série synchrones courantes telles que les interfaces 2 fils (SCL, SDA) et 4 fils (CS, SCK/CLK, MISO/SDI/DIN et MOSI/SDO/DOUT).
 

Offline flachyjoe

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #105 on: November 16, 2024, 11:17:23 am »
The chipset is CH341B 406725D24
 

Offline Tantratron

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #106 on: November 16, 2024, 11:31:37 am »
It seems lot of CH341x variants after all  :)
 

Offline Ian.M

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #107 on: November 16, 2024, 11:36:05 am »
Ch341B shares a datasheet with CH341A: http://bitsavers.informatik.uni-stuttgart.de/components/wch/_dataSheets/CH341DS1.PDF
and has exactly the same power pin specifications and I/O voltage levels.

If with the jumper removed, you still have >3.3V signal levels when idle on the SPI pins (1-4 of the  same header as the jumper), or have 5V on pin 28 (Vcc) of the CH341x IC (corner nearest board edge and ZIF socket), you need to do the mod.
 

Offline flachyjoe

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #108 on: November 16, 2024, 12:33:52 pm »
3.332V at the 2 places so it's good.  :)

Thank you two!
 

Offline Tantratron

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #109 on: November 17, 2024, 10:58:47 am »
Hello @Ian.M and @flachyjoe

First question to Ian because I'm bit confused or lost plus I'm not native english so I did not fully understand what exact voltage test, what pins should be done

If with the jumper removed, you still have >3.3V signal levels when idle on the SPI pins (1-4 of the  same header as the jumper), or have 5V on pin 28 (Vcc) of the CH341x IC (corner nearest board edge and ZIF socket), you need to do the mod.

There should 2 tests, one with the jumper installed and then with no jumper, correct ?

As mentioned earlier, I've bought from amazon the CH341A programmer board. Wether the jumper is installed, I do have always +5V  on these pins: CH431-28 ZIF-1 ZIF-2 ZIF-5 and ZIF-6. By ZIF here I mean, the socekt plug dedicated for 25XX then on this same connector, I always have +3.3V on ZIF-3 ZIF-7 and ZIF-8

What do you mean by 3.3V then what do you mean by 1-4... do you mean 5V, do you mean pin measurement voltage between ZIF-1 (CS) and ZIF-4 (GND) ?

3.332V at the 2 places so it's good.  :)

Second question for flachyjoe, can you detail exactly what places (which pins) did you get 3.3V ?

You said to purchased on eBay in France this model https://www.ebay.fr/itm/324505422583 . The picture and title of the french eBay-vendor shows CH341A but you said the item in your hand has CH341B. Do you confirm it has 3.3V on all ZIF pins and Chip-28 so you do not need to make any modification ?

Third and last question to Ian,

When reading the beginning of the thread started in 2017, I see that you modified and edited part your post #3

I do not know what was the description to modify back then, I just want to make sure that the easiest way to modify and make sure no 3.3V flash chip to be fried consists to do this re-wiring No track cuts, just lift pin 28 (easy because its near the board edge with nothing in the way) and run a wire from the lifted pin across to pin 9, and on to the 3.3V regulator output.

Thank to take time clarifying your posts so it will safe. The reason I ask is first I'm not native english, second the thread has been going with 5 pages with other modifications so I prefer to really have say a 2024 final update.

Albert

 

Offline Ian.M

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #110 on: November 17, 2024, 12:31:10 pm »
See https://www.onetransistor.eu/2017/08/ch341a-mini-programmer-schematic.html

I said measure with jumpers removed, because some mods/versions of the CH341x ZIF programmer board use a jumper for VCC selection usually by shorting out the 3.3V regulator for 5V operation.   This is *NOT* ideal as the CH341x chips need 3.3V for their USB interface to operate correctly, and if  the dropout voltage of their internal regulator supplying V3 (pin 9) from Vcc (pin 28) is too high, when Vcc is at 3.3V the reduced voltage on V3 can cause USB communication errors, and/or data corruption.  The datasheet says to link Vcc and V3 to bypass the internal regulator when Vcc is 3.3V.

To determine what mods if any are needed for your programmer, its easiest to use the USB shell as a ground point and measure the I/O pins 1-4 on the header beside the ZIF socket near the same board edge as the crystal.   You can also easily measure Vcc at pin 28, but the risk of damage from a short if your probe slips is much higher.  Don't try to measure at the ZIF socket itself, as the contacts aren't easily accessible from the top with a multimeter probe.  Note that the usual parking (storage) position of the jumper on pin 1 & 2 of the other header shorts ACT# to ground.  This does no harm because there is a series resistor between the header's ACT# pin and the CH341x.

Three possible conditions will be found when measuring a powered, idle CH341x programmer with no jumpers fitted.  Either Vcc and the SPI I/O pins will be at 5V, or at 3.3V or at 0V (if the design version or mod requires a jumper fitted to supply Vcc power).

If you get either 3.3V or 5V and your memory chips aren't the same voltage, you need to do a mod.  This topic is about modding the 5V version down to 3.3V, either permanently or switchably.  If you get 3.3V and need 5V its a different mod, not covered yet here.

If you get 0V, *either* your programmer is modded or a different version and you should follow its supplier's instructions for what jumpers to fit for 3.3V or 5V operation *or* its not getting power from the USB, or its faulty.  As it has a power LED, its easy to see if its getting power. 

My reply #3 was only updated to fix a broken link to the CH341x datasheet.  Many have modified this programmer following my suggestion in #3, and some have even made videos about it.  The key to success is to use desoldering braid (aka: solderwick) to remove as much solder as possible from pin 28 before lifting it, only lift it far enough to break the surface tension of the molten solder between it and the pad so it no longer bridges,  and to use *THIN*, preferably solid core wire, thinner than the pin so you don't stress it too much when handling the wire.   I prefer Kynar insulated silver plated solid core 30 AWG wirewrap wire, but others prefer magnet wire.  It can be very difficult to remove the varnish insulation from thin magnet wire without damaging the wire, and Kynar insulation is fairly tough, so the wire will be pulled on when you strip the end, so in either case, to avoid pulling pin 28 off the IC, prepare the wire to length and bent to shape, and get both ends tinned before you solder it to the board.  Using electronics grade flux will make all the desoldering and soldering operations easier.

I also discussed a 5V/3.3V switchable mod in reply #55.  There are others that *DON'T* use a DPDT switch, but many of those don't power V3 properly when switched to 3.3V so even if the CH341x still enumerates correctly, may cause hard to trouble-shoot programming errors.  If the other mod gives less than 3.1V or greater than 3.6V on V3 (pin 9) expect trouble!
 
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Offline Tantratron

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #111 on: November 17, 2024, 04:19:42 pm »
See https://www.onetransistor.eu/2017/08/ch341a-mini-programmer-schematic.html

I said measure with jumpers removed, because some mods/versions of the CH341x ZIF programmer board use a jumper for VCC selection usually by shorting out the 3.3V regulator for 5V operation.   This is *NOT* ideal as the CH341x chips need 3.3V for their USB interface to operate correctly, and if  the dropout voltage of their internal regulator supplying V3 (pin 9) from Vcc (pin 28) is too high, when Vcc is at 3.3V the reduced voltage on V3 can cause USB communication errors, and/or data corruption.  The datasheet says to link Vcc and V3 to bypass the internal regulator when Vcc is 3.3V.

To determine what mods if any are needed for your programmer, its easiest to use the USB shell as a ground point and measure the I/O pins 1-4 on the header beside the ZIF socket near the same board edge as the crystal.   You can also easily measure Vcc at pin 28, but the risk of damage from a short if your probe slips is much higher.  Don't try to measure at the ZIF socket itself, as the contacts aren't easily accessible from the top with a multimeter probe.  Note that the usual parking (storage) position of the jumper on pin 1 & 2 of the other header shorts ACT# to ground.  This does no harm because there is a series resistor between the header's ACT# pin and the CH341x.

Three possible conditions will be found when measuring a powered, idle CH341x programmer with no jumpers fitted.  Either Vcc and the SPI I/O pins will be at 5V, or at 3.3V or at 0V (if the design version or mod requires a jumper fitted to supply Vcc power).
Hello Ian, ok many thanks now I fully understand your explanations, guidance plus is now clear to me what you meant by I/O pins 1-4 which are respectively SCK, CS, MOSI and MISO. After removing the unique yellow jumper, my DMM reads respectively +5V on I/O pins 1-4 then with caution and concentration, I've measured as well Vcc from CH341A-28 to be 5V hence MOD is required.

I did measure again directly the 8 pins of the ZIF socket, in my case no problem to DMM which corresponds to my yesterday post (see the picture and markings). We have confirmation that the 4 signals in charge of SPI are 5V which is the threat but note that the SO8 flash memory remaining 3 pins are all 3.3V (WP, Vcc and Hold) where the 8th pin is of course GND. The Vcc pins in the ZIF is 3.3V whereas the Vcc on CH341-28 is 5V so no idea if this logical per design or confirms the risk to fry a 3.3V flash memory. It is really strange that from the ZIF connector (total 8 pins) some of the pins read 3.3V and others 5V, at least in my recently acquired board.

It would interesting to have confirmation from @flachyjoe that his CH341B board offers always 3.3V on all the pins even though the french eBay vendor had pictures and title with CH341A. This would his board has been modified at factory and he got lucky with this eBay purchase in France.

My reply #3 was only updated to fix a broken link to the CH341x datasheet.  Many have modified this programmer following my suggestion in #3, and some have even made videos about it.  The key to success is to use desoldering braid (aka: solderwick) to remove as much solder as possible from pin 28 before lifting it, only lift it far enough to break the surface tension of the molten solder between it and the pad so it no longer bridges,  and to use *THIN*, preferably solid core wire, thinner than the pin so you don't stress it too much when handling the wire.   I prefer Kynar insulated silver plated solid core 30 AWG wirewrap wire, but others prefer magnet wire.  It can be very difficult to remove the varnish insulation from thin magnet wire without damaging the wire, and Kynar insulation is fairly tough, so the wire will be pulled on when you strip the end, so in either case, to avoid pulling pin 28 off the IC, prepare the wire to length and bent to shape, and get both ends tinned before you solder it to the board.  Using electronics grade flux will make all the desoldering and soldering operations easier.

Many thanks for de-soldering and re-solding mod instructions, I see all the points
 

Offline Tantratron

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #112 on: November 17, 2024, 05:51:01 pm »
P.S. When buying from amazon the CH341A, the seller sent me a link with manual and drivers for Windows. I did not read neither used these since i'm using MacOS with specific driver and software from Github for CH341A and flashrom. Anyway I now read one manual and it does warm about the 5V risk then points out to that  link that you might probably know. There is YouTube video which shows the same modification by ian but I read some comments, here are some extract.

Extract 1: Okay, this is really funny. This video shows how to bring level down to 3.3 V, but DrShock has a Youtube with his CH341 only providing 3.3 volt and shows how to modify his version of the board to bring it up to 5.0 V. Apparently, DrShock needs the 5V for automotive chip programming, while the 3.3V is needed for PC BIOS chips. Perhaps you guys can just trade boards? I'd say there are 2 versions out there and just be sure you get the one for your particular chip programming application. This is very interesting topic, though. I used a chip programmer with a sewing needle to 3.3 V power to re-program a 2015 Apple MacBook Prom to unlock it with chip in-place on board with a ribbon cable that attached to a SAM socket directly on the logic board. Nice and clean and no soldering. Just had to hold the pin steady for a few minutes to do the read, and then again to do the write. I'm typing this on that computer. Battery and power disconnected from logic board, sewing needle attached to a 3.3 V lead from an old PC power supply.

Extract 2: Thank you very much! my CH341B  worked badly for writing a Winbond 25Q64FV now its works really well !!! my problem is solved thanks you! ( I buy a 341A on ebay and i receive a 341B, but it's work now!!)

It would be really interesting to know if the CH341B purchased by flashyjoe does only 3.3V

Then why if this 5V - 3.3V issue is known for years, the chinese still continue to sell and not fix the design ?
 

Offline Tantratron

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #113 on: November 20, 2024, 10:05:40 am »
Maybe one last question regarding USB-CH341A programmer to read or write the SPI NOR memory (25 serie).

In another project, I need to USB interface through a VGA-i2c port connected to a LCD panel processor which is not tolerant to 5V.

Do you confirm the 5V versus 3.3V topic does threat the 24 serie ZIF connector, in other words wether the 4 pins 25 serie or the 4 pins 24 serie, same threat hence MOD solves both scenario ?

 

Offline Ian.M

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #114 on: November 20, 2024, 12:38:16 pm »
VESA DDC I2C (on VGA ports) used 5V signal levels - see page 18 of https://www.eevblog.com/forum/projects/i2c-over-cat5e-problem/?action=dlattach;attach=185318

If you are using VGA port I2C, for a 3.3V (or lower) target, you need one of these: https://www.adafruit.com/product/757 or equivalent from Amazon, Ebay or the usual far east 'eBazaar' suppliers.
It should follow Philips AN97055, with one N-MOSFET per signal line.  It needs a 3.3V supply to biass the MOSFET gates, but that can usually be tapped from the target device as very little current is needed.

The various CH341x 3.3V mods are all good for both SPI and I2C.

The switchable version of the CH341x mod can be wired to auto-set the target Vcc voltage, so you dont need to jumper 3.3V to 5V to short out the regulator when programming 5V devices.   This is actually a simpler mod - lift Vcc (pin 28) and link it to the regulator output.  Wire a SPST switch, common to regulator output, one end to V3 (pin 9) and the other to the regulator input (+5V).  With the switch in the 5V position, confirm the regulator does not get hot, and that there is 5V at the programmer socket Vcc pins.

Ideally replace the zero ohm link in the R1 (marked F1) position on the CH341x programmer PCB with a 250mA polyfuse to protect your PC if the programmer Vcc gets shorted in 5V mode.
« Last Edit: November 20, 2024, 12:41:24 pm by Ian.M »
 

Offline FazzaGBR

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #115 on: November 20, 2024, 02:28:44 pm »
I purchased one of these a while back, such great value for money and I'm so glad the topic of the voltage came up on a YouTube video I saw and when I checked the voltage on my device it was wrong so did the lifting up of the pin and soldering a wire to the 3.3V supply and hey presto it was safe to use!
 

Offline Tantratron

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #116 on: November 20, 2024, 02:47:31 pm »
VESA DDC I2C (on VGA ports) used 5V signal levels - see page 18 of https://www.eevblog.com/forum/projects/i2c-over-cat5e-problem/?action=dlattach;attach=185318

If you are using VGA port I2C, for a 3.3V (or lower) target, you need one of these: https://www.adafruit.com/product/757 or equivalent from Amazon, Ebay or the usual far east 'eBazaar' suppliers.
It should follow Philips AN97055, with one N-MOSFET per signal line.  It needs a 3.3V supply to biass the MOSFET gates, but that can usually be tapped from the target device as very little current is needed.

The various CH341x 3.3V mods are all good for both SPI and I2C.

The switchable version of the CH341x mod can be wired to auto-set the target Vcc voltage, so you dont need to jumper 3.3V to 5V to short out the regulator when programming 5V devices.   This is actually a simpler mod - lift Vcc (pin 28) and link it to the regulator output.  Wire a SPST switch, common to regulator output, one end to V3 (pin 9) and the other to the regulator input (+5V).  With the switch in the 5V position, confirm the regulator does not get hot, and that there is 5V at the programmer socket Vcc pins.

Ideally replace the zero ohm link in the R1 (marked F1) position on the CH341x programmer PCB with a 250mA polyfuse to protect your PC if the programmer Vcc gets shorted in 5V mode.

The reason i'm asking is related to firmware reading and/or writing this LCD driver board based on RTD2660 processor. The board has a SPI NOR flash memory which is clearly 25xx (3.3V) then one option is to use the CH431A programmer and grabber to flashrom, this is why I purchased the CH431A. Another approach which is documented here consists of using an adafruit FT232H and make specific wiring as shown. The LCD driver board has VGA connector but its 2 pins dedicated to SDA/SCL are directly connected to the RTD2660H panel processor via 100R with 4.7K resistor.

So there are 2 ways to hack or flash the SPI eeprom: either direct via CH431A programmer or indirect via the VGA-i2c where the RTD2660H will internal route the commands to the actual SPI eeprom. This is why I was wondering if OK to use the CH431A with modification to explore hacks.

I do know from reading the datasheet of RTD2660 than its pins 58 (SCL) and 59 (SDA) says not 5V power tolerant so we kind of go back to the 3.3V story with CH431A except here I'd use its 24xx outputs instead of using the FT232H interface.

What would be unique or universal modification to make sure wether 25xx outputs or 24xx would be always 3.3V
« Last Edit: November 20, 2024, 02:59:00 pm by Tantratron »
 

Offline Ian.M

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #117 on: November 20, 2024, 03:08:03 pm »
A cheaper alternative to the Adafruit FT232H board is CJMCU FT232H breakout board from the usual far east suppliers.  Same chip but no fancy I2C mode switch or Stemma connector, so you have to patch D1 and D2 together, and probaby add pullups for SDA and SCL to either 3.3V or 5V yourself.

Most programming or configuration software that uses a FT232H to 'talk' I2C cant use a CH341x and visa versa.  Check what interface ICs the software you need to use supports.
 
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Offline Tantratron

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #118 on: November 20, 2024, 03:33:27 pm »
Most programming or configuration software that uses a FT232H to 'talk' I2C cant use a CH341x and visa versa.  Check what interface ICs the software you need to use supports.

Many thanks Ian for this hint and guidance so i'll go after a FT232H board to VGA-i2c dialog with the RTD2660 re-directing R/W to the external SPI NOT memory and CH431A with 5V-3.3V modification to directly R/W with grabbers the SPI NOR memory. Normally I should get the same binary image unless the RTD2660 is bricked.

Merci beaucoup
« Last Edit: November 20, 2024, 05:40:07 pm by Tantratron »
 

Offline Ian.M

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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #119 on: November 20, 2024, 06:35:09 pm »
That should work.  The FT232H chip has 3.3V logic levels but 5V tolerant so can be used with either 5V or 3.3V SPI and I2C with no problems. 

N.B. The CJMCU FT232H board I suggested does *NOT* have a seperate 3.3V regulator, but the FT232H has one internally, good for only a few tens of mA - enough for I2C pullups and small 8 pin EEPROMs, but *NOT* enough for any target board and maybe not enough for big Flash memories.  Be careful *NOT* to short its 5V, its 'raw' unfused USB Vbus and if you short it, either it will burn the board or maybe damage your PC.
 
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Re: CH341A Serial Memory Programmer Power Supply Fix
« Reply #120 on: January 07, 2025, 02:19:01 am »
The 5V / 3.3V myth perpetuated by the internet was evaluated and debunked a few years ago.  No need to mod the CH341A.  Just use it . . .

Have a look at this video created by Sorin (Electronics Repair School) analyzing the issue in detail:  https://youtu.be/J8-Sh7DjiXw
 


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