TELink B91 Quick Start Manual page 4

USB to TTL serial cable
Connect the DUT and USB-TTL together.
TXD -> PB3 (DUT)
RXD -> PB2 (DUT)
GND -> GND (DUT)
Refer to "Burning and Debugging Tools for all
file to the board.
Hardware
Series" to download the binary
Telink Proprietary 4