Note On Using P12/Txd0 - Renesas RL78/G22 User Manual

RL78/G22 Fast Prototyping Board 6. Handling Precautions
6.5

Note on Using P12/TxD0

When the power is turned on or immediately after release from resetting of the USB-to-serial converter of this
product, if a user program which starts the output of the UART transmission to the P12/TxD0 line is written to
the target MCU before the host PC recognizes the USB-to-serial converter as the COM port, the operation of
the USB-to-serial converter may be unstable and prevent connection to the Renesas Flash Programmer or
terminal software.
In such cases, turn on the power (connect the USB cable) while pressing the reset switch, wait about 3
seconds until the host PC recognizes the USB-to-serial converter as the COM port, and release the reset
switch. Otherwise, reset the USB-to-serial converter (by briefly short-circuiting J15 and then restored it to
open-circuit) while pressing the reset switch, wait about 3 seconds until the host PC recognizes the USB-to-
serial converter as the COM port, and release the reset switch.
Finally, erase the user program by using the Renesas Flash Programmer.
R20UT5121EJ0100 Rev. 1.00 Page 32 of 35
Nov.16.22