nesdev.com

Wikipedia says the Super FX can upload graphics from the cartridge to VRAM. Shouldn't therefore the PA lines on the connector be bidirectional?

There is only one bus master in the SNES, and that's the S-CPU and its DMA unit. The SFX is not what's doing the uploading.

I always believed that DMA can transfer tiles directly from the rom to the vram... and with an sfx we still have the dma doing the same job.

The SFX don't do anything in that way.

It can.

DMA transfers data from one bus to the other. ROM and cart RAM are on bus A, and the PPU's VRAM data port is on bus B. The console's WRAM is on bus A or bus B (but not both at once). DMA from cart RAM to WRAM pauses the 65816, and I think the GSU is paused as well.

OP's link is broken. Anyone have a mirror link?

Not sure if it's the most recent version

I think the commas went away, or something.

https://wiki.superfamicom.org/schematics-ports-and-pinouts

Here's the last version of snes_schematic_color I have, four minor revisions newer than what sanni posted-

If you click on that link you posted, you'll see all the schematic file links are broken.