In plain language
Transition Minimised Differential Signalling sends video over three data lanes plus a separate clock, with the clock speed rising as the picture gets more demanding. 4K60 4:4:4 needs a 600MHz clock, which works out at 18Gbps — the ceiling of the TMDS era.
Why it matters in your setup
Most content still runs over TMDS. 4K60 HDR from a streaming box or a Blu-ray player does not need FRL. So when a status readout shows a TMDS clock rather than an FRL rate, that is usually correct rather than a fault.
It becomes a clue when you expected more. If you asked for 4K120 and the link reports TMDS, the two ends never agreed to switch to FRL at all — which points at the EDID or at a device in the chain, not at the cable.
One practical note: TMDS termination on a graphics card can interact badly with hot-plug behaviour, a known source of odd PC-side symptoms.
What the DR HDMI 8K does with it
The DR HDMI 8K reports the TMDS clock, the clock ratio and the scramble state alongside the FRL figures, so you can tell at a glance which signalling mode the chain is actually using. Firmware 1.2 fixed a hot-plug issue on GPUs when TMDS termination is active.
Need the hardware?
Open the DR HDMI 8K product page on HDfury.uk.