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:

 J-Link>SetHWFC Enable/Disable/Force

• Enable: Default. Enables hardware flow control and runtime auto-detection
• Disable: Disables hardware flow control (never used)
• Force: Enables hardware flow control and bypasses runtime auto-detection (RTS is kept driven and CTS is kept sampling)