Hi,
My CAC-1088 works at 4K 60 Hz RGB but won't do 4K 120 Hz. Is there a firmware update for it, or any other advice?
Setup
- GPU: AMD Radeon PRO W7700 (DisplayPort output), driver AMD Software PRO Edition 24.Q2
- OS: Windows 11 Pro 24H2
- Adapter: CAC-1088, plugged directly into the GPU
- Cable: Club3D CAC-1371 Ultra High Speed HDMI, 1 m
- Display: LG OLED48C2 (webOS 24), HDMI 1, HDMI Deep Colour on, input icon set to PC
GPU capability
- The Radeon PRO W7700 has 4x DisplayPort 2.1 (UHBR13.5) outputs, up to 52.2 Gbit/s, with DSC support. AMD rates it for up to 8K 120 Hz with DSC.
- 4K 120 Hz over DP 1.4 HBR3 is well within its capability, and with this adapter the link already trains at HBR3 (8.1 Gbps x 4).
- The driver lists 4K 120 Hz and 100 Hz from the TV's EDID, so the GPU isn't refusing the mode. It fails only when driving it through the adapter.
What I've found
- 4K 60 Hz RGB 4:4:4 works at 8 and 10-bit. The DP link trains at HBR2 for 8-bit and HBR3 (8.1 Gbps x 4) for 10-bit.
- Selecting 120 Hz or 100 Hz in Windows (8 bpc RGB) drops the signal and it reverts.
- A custom 4K 120 Hz reduced-blanking timing (3920 x 2250 total, 1,058.4 MHz pixel clock, about 25.4 Gbps, so within HBR3 without DSC) is rejected by the AMD driver with "The custom resolution settings are not compatible with this display".
- The TV's EDID (below) advertises 4K 120 Hz (VIC 118), a 1,190 MHz maximum pixel clock in the range limits, and HDMI 2.1 FRL at 48 Gbps. So the TV side looks correct.
- A full cold restart (TV unplugged from the wall, adapter re-seated) made no difference, and the EDID was identical afterwards.
- I've tried two different DP outputs on the GPU.
To me this looks like the adapter isn't reporting its HDMI 2.1/FRL or DSC capability to the GPU, so the driver limits it to an HDMI 2.0-level pixel clock. I've seen a thread here where a firmware update fixed the same problem with a CAC-1087 and an LG C2.
If firmware is available, I'm happy to send the adapter's serial and purchase details privately.
TV EDID (exported from AMD Software):
00 FF FF FF FF FF FF 00 1E 6D C8 C0 01 01 01 01
01 20 01 03 80 A0 5A 78 0A EE 91 A3 54 4C 99 26
0F 50 54 A1 08 00 31 40 45 40 61 40 71 40 81 80
D1 C0 01 01 01 01 08 E8 00 30 F2 70 5A 80 B0 58
8A 00 40 84 63 00 00 1E 6F C2 00 A0 A0 A0 55 50
30 20 35 00 40 84 63 00 00 1E 00 00 00 FD 00 18
78 1E FF 77 00 0A 20 20 20 20 20 20 00 00 00 FC
00 4C 47 20 54 56 20 53 53 43 52 32 0A 20 01 64
02 03 66 F1 5D 61 60 76 75 66 65 DB DA 10 1F 04
13 00 00 03 02 12 20 21 22 00 5D 5E 5F 62 63 64
3F 40 2C 09 57 07 15 07 50 57 07 01 67 04 03 6E
03 0C 00 10 00 B8 44 24 00 80 01 02 03 04 6D D8
5D C4 01 78 80 6B 00 00 00 C3 33 05 E2 00 CF E3
05 C0 00 E3 06 0D 01 E2 0F FF EB 01 46 D0 00 48
0A 7E 86 60 76 94 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 CFThanks,
Tom