Yes, 870 chipset based on RX 780, but the codename 870 chipset is RX880 and he have something changes.
870 chipset:
Codenamed RX880;
Single AMD processor configuration;
One physical PCIe 2.0 x16 slot, one PCIe 2.0 x4 slot and two PCIe 2.0 x1 slots, the chipset provides a total of 22 PCIe 2.0 lanes and 4 PCIe 2.0 for A-Link Express III solely in the Northbridge;
HyperTransport 3.0 and PCI Express 2.0.
770 chipset:
Codenamed RX780, final product name revealed by ECS;
Single AMD processor configuration;
One physical PCIe 2.0 x16 slot, one PCIe 2.0 x4 slot and two PCIe 2.0 x1 slots, the chipset provides a total of 22 PCIe 2.0 lanes and 4 PCIe 1.1 for A-Link Express II solely in the Northbridge;
HyperTransport 3.0 and PCI Express 2.0.
So still I worry about what the program says that I have is the north bridge RX780 at 870 chipset? I just immediately ran to check the code name for my northbridge and I'm excited:D