J-Link OB SAM3U NordicSemi
This J-Link model supports VCOM.
This J-Link OB supports max. 1 MBaud. The internal divider is calculated as follows:
Baudrate = 96000000 / Div * 16; Div = 96000000 / (Baudrate * 16);
Note: The real baudrate and the selected one should not deviate more than 3% to guarantee proper communication on 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:
Note: This setting gets active immediately and survives a power-cycle of J-Link.
- 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)