I always get noUlink device found error.
closed as unclear what you're asking by Michel Keijzers, dim, Voltage Spike, winny, PeterJ Jun 11 '18 at 11:50
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Reference Application note:
Please note that, yes it is possible to program the microcontroller using USB to TTL cable you have got.
You need to use ST software on the computer for that which will connect to the MCU through the specific UART interface on the board. The application note gives idea on which UART ports can be used and also about the ST software to be used. This information and Boot Pin configuration setting ( from application note again) should solve it.
Any reason why you have to use keil software only for programming?
If you are planning to debug the code, then you have to have a debugger whether standalone (ST Link, JLink ) or a Nucleo or other ST boards which have a dedicated STLink part in it.
You need something like a Segger J-Link - rather expensive. Cheapest solution is to buy an STM32 Discovery board (virtually any of them will do) which has an on-board programmer, and use that to program your device. It will have a connector and jumper which enable it to be used with external devices.
I agree with @Duskwuff. I bought the ST-Link V2 a few months ago, and it was around $20. It's very simple to use, and almost works plug-and-play. No fumbling around with custom headers and having another big annoying PCB on your table. ST-Link V2 is the way to go.