VERSION 1.9
J120 (38198-X)
Appendix A
Bypass of UART0 (watchdog MCU)
The schematics above show the circuit details of the UART0/2 connector (J7). In the standard UART0
configuration the UART0 port of the TX1/TX2 is connected to the MCU. The MCU is programmed to tunnel all
output on UART0 to it second UART port, which then connects to the J7 connector. The MCU was introduced as
an option with rev 6 and became a standard feature with rev 7.
If you experience problems with the UART0 port and your use case requires a direct connection to UART0 the
MCU may be bypassed by the following steps:
1. please flash the MCU (STM32F042) with the J90-J140-MCU-UART-OFF firmware. This disables the UART ports
of the MCU so that it may be bypassed. Alternatively the MCU may be removed.
2. please populate RN1 with a 10 Ohm resistor network
(Panasonic: EXB-24V100JX, Digikey: Y5100CT-ND,
Auvidea: 25151), to connect the UART0 port of the TX1/
TX2 to J7. Please note that this requires very good
soldering skills and it should be performed by our
technicians. Please contact our support team.
AUVIDEA GMBH
TECHNICAL REFERENCE MANUAL
26