Hi!
Is Segger J-Link/J-Flash using a push-pull driver or open-drain on the SWDIO pad?
Reason for my question is that the uController we are interfacing as an internal pull-down on SWDIO - which is against the recommendation in the ARM Debug Interface Architecture Specification, section 4.4.2 where a pull-up is required.
When we put an external pull-up there is the problem of getting an intermediate voltage level (due to the internal pull-down) on SWDIO and cross-current. So, we want to get rid of the external pull-up and use only the pull-down. My understanding is, that the pull resistor is required to avoid SWDIO floating when no debugger is connected, which is also achieved by a pull-down. A pull-up is required in case the debugger is using an open-drain driver instead of push-pull.
We already tried removing the external pull-up an Segger J-link still works, so I guess J-lInk uses a push-pull driver - just wanted to get the confirmation for this.
Thanks,
Christian
Is Segger J-Link/J-Flash using a push-pull driver or open-drain on the SWDIO pad?
Reason for my question is that the uController we are interfacing as an internal pull-down on SWDIO - which is against the recommendation in the ARM Debug Interface Architecture Specification, section 4.4.2 where a pull-up is required.
When we put an external pull-up there is the problem of getting an intermediate voltage level (due to the internal pull-down) on SWDIO and cross-current. So, we want to get rid of the external pull-up and use only the pull-down. My understanding is, that the pull resistor is required to avoid SWDIO floating when no debugger is connected, which is also achieved by a pull-down. A pull-up is required in case the debugger is using an open-drain driver instead of push-pull.
We already tried removing the external pull-up an Segger J-link still works, so I guess J-lInk uses a push-pull driver - just wanted to get the confirmation for this.
Thanks,
Christian