They are chip selects and become active (low) when an address in the appropriate range is accessed. So PCS0 covers the range 0-127, PCS1 is 128-255, etc. The base address is configurable on a 1K boundary, so suppose you configure the base address for 0x1000 then PCS0 is active if you access 0x1000 to 0x107F, PCS1 from 0x1080 to 0x10FF, etc.
The base address is set via the upper 9 bits in the PACS register (that is, bits 15..6). The lower 3 bits determine the wait states and used of RDY.
You don't directly drive the pins. If you want I/O that you can set to a state and have it stick then you would just a latch connected to the data bus (even jut one or two bits would be fine) and then use PCSx and WR to clock in the data.