IBM 5161 - Extender Card - Switch Settings
Memory (ROM/RAM) operations between the CPU (in host computer) and the 5161, are slowed by the extender and receiver cards. Because of that, IBM require that a wait state be invoked for operations involving any memory in the 5161. The switches on the extender card control the memory address range in which the extender card signals the CPU to add a wait state.
1 = ON
0 = OFF
NOTE: The EFFFF upper limit is designed into the extender card.
It is so that CPU reads of the ROMs on the 5160 motherboard do not result in a wait state.
There is an XT-class hard disk controller in the 5161.
The controller's ROM is addressed C8000 to C9FFF, and is the only memory in the 5161.
Therefore you need to have the extender card generate a wait state for address range C8000 to C9FFF.
The appropriate extender card switch setting would be 0011, i.e. address range C0000 to EFFFF.
Note that in this example, although not required, address range C0000 to C7FFF and address range CA000 to EFFFF, also invoke a wait state.
So, if there is an expansion card in the host computer that has a ROM that starts at address C0000, reads of that ROM will be unnecessary slowed by a wait state.
An unfortunate side effect.
You have 256 KB of RAM on the 5160 motherboard (addressed 0 to 3FFFF), and 384 KB of RAM in the 5161 (addressed 40000 to 9FFFF).
Therefore you need to have the extender card generate a wait state for address range 40000 to 9FFFF.
The appropriate extender card switch setting would be 1011, i.e. address range 40000 to EFFFF.
Note that RAM in the 5161 is a poor example, because it is to be avoided, for performance reasons. In the 5161, RAM will be slowed by the wait state.