J-Link OB SAM3U NordicSemi

VCOM functionality

This J-Link model supports VCOM.

Pin driving policy

The following pins are available on this OB:

• OB_Tx (driven by J-Link OB)
• OB_Rx (driven by target)
• CTS (driven by target. LOW == Target ready to receive data)
• RTS (driven by J-Link OB. LOW == J-Link OB ready to receive data)

J-Link OB starts driving its VCOM output pins as soon as it receives a "set baudrate" command. This command is send by the PC as soon as a COM port is opened. Unfortunately, there is no specific command / packet etc. send by the PC in case a COM port is opened. Therefore the "set baudrate" approach is the only one to detect COM port activity.

J-Link OB stops driving the RTS pin if J-Link OB detects that hardware flow control is not used on the target side.

Hardware flow control support

Hardware flow control is supported by this J-Link OB. By default, J-Link detects at runtime if the target uses flow control or not. This is done as follows:

• If CTS is detected as HIGH (Target not ready) before the first character is sent by J-Link OB, the pin is assumed to be not used by the target and flow control on the J-Link side gets disabled (CTS is ignored from now on, J-Link stops driving RTS)

Force or disable hardware flow control

It is possible to configure J-Link OB to bypass the hardware flow control auto-detection in the firmware and assume that hardware flow control is always or never used. This can be done via J-Link Commander and the following command:

 <!-- This entry will overwrite the existing device entry in the J-Link software, so that a custom flash algorithm is used for the internal flash -->
   <ChipInfo Vendor="ST" Name="STM32F767ZI" Core="JLINK_CORE_CORTEX_M7" />
   <FlashBankInfo Name="Internes Flash" BaseAddr="0x08000000" MaxSize="0x00200000 " Loader="ST_STM32F7xxxx_2MB_DualBank.elf" LoaderType="FLASH_ALGO_TYPE_OPEN" />
 </Device>