CH341A is an USB interface chip that can emulate UART communication, standard parallel port, memory parallel port and synchronous serial (I2C, SPI). The chip is manufactured by Chinese company. CH341A is used by some cheap memory programmers. The IC is somehow limited in this configuration, because the programmer makes use only of the SPI and I 2C interface and leaves a lot of pins unconnected. A popular device is the black that you can buy for 2 to 5 USD. The problem with these devices is that you get them without any documentation or software.

FPGA configuration Flash PROMs — Xilinx (XC18Vxx, XCFxxS) Atmel ATmega; Serial EEPROM and Flash memories. I2C (24LCxx) Microwire (93LCxx) SPI EEPROM (25Cxx) SPI Flash EPROM (M25Pxx, M45PExx, etc.) In-Circuit Serial Programmer Software Supported Devices Most devices are supported by the included UP programming software.

Drivers are available from manufacturer's website (but the site is written in Chinese). Also, some source codes are available from manufacturer. There are open source applications that support this programmer. But, first of all, let's have a look at the hardware. Photo of the black CH341A Mini Programmer A quick look at the board reveals the main electronic parts used: CH341A, a 12 MHz crystal required by the chip, a 3.3V regulator, two 7 pin headers and the ZIF ( zero insertion force) socket. The programmer can be bought with additional sockets and adapters, some of them with voltage shifting circuits. After some searching I found a schematic of a CH341A based programmer, but it wasn't exactly right and complete.

It didn't have the pinheaders on the sides of the ZIF socket which I wanted to know what they are for. I took the multimeter and started to trace lines on the programmer PCB until I got a complete schematic. The schematic is quite simple, based on datasheet. Schematic of the black CH341A Mini Programmer I also found (a seller on AliExpress).

Their offered a the PCB design of the device (only top side, however). CH341A Mini Programmer PCB (by WAVGAT/AliExpress) Now, let's return to the schematic and analyze it a bit. The chip is powered from 5V, so its I/O ports will also use 5V. Basically this is a 5V device. The problem is that any memory you fit in the socket will be powered from 3.3V. And this seems to be the only function of the 3.3V regulator (besides the 3.3V pin on the SPI connector). I don't know why the designer even used a regulator, if it didn't provide a switch to choose between 3.3V or 5V levels and supply.

By, we can see that the manufacturer recommended to connect a 0.47 uF capacitor between RSTI (pin 2) and VCC for improved stability. There is none on this board. Anyway, I used the device with I2C EEPROMS (3.3V and 5V) compatible and also SPI FLASH memories (3.3V devices) without any issues. For improved reliability and to avoid burning memory chips, I highly recommend using a level shifter. In order to turn this programmer into a 3.3V device, you could cut the 5V line from VCC pin (28) and tie it to the 3.3V output from regulator. You will also need to connect V3 pin (9) to VCC (3.3V). User johnmx from EEVblog Forum has succeeded in.