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IBM 5161  -  Extender Card  -  Switch Settings


Controls the memory address range in which the extender card signals the CPU to add a wait state.

  1 = ON
  0 = OFF

Switches 1234	Address range in which extender card   will generate a wait state
1111	00000 to EFFFF   (    0 K to 960-1 K)
1110	10000 to EFFFF   (  64 K to 960-1 K)
1101	20000 to EFFFF   (128 K to 960-1 K)
1100	30000 to EFFFF   (192 K to 960-1 K)
1011	40000 to EFFFF   (256 K to 960-1 K)
1010	50000 to EFFFF   (320 K to 960-1 K)
1001	60000 to EFFFF   (384 K to 960-1 K)
1000	70000 to EFFFF   (448 K to 960-1 K)
0111	80000 to EFFFF   (521 K to 960-1 K)
0110	90000 to EFFFF   (576 K to 960-1 K)
0101	A0000 to EFFFF   (640 K to 960-1 K)
0100	B0000 to EFFFF   (704 K to 960-1 K)
0011	C0000 to EFFFF   (768 K to 960-1 K)
0010	D0000 to EFFFF   (832 K to 960-1 K)
0001	E0000 to EFFFF   (896 K to 960-1 K)
0000	This setting disables all wait state generation by the extender card

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.


EXAMPLE:

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 in this example, memory access in address range A0000 and EFFFF will also result in a wait state.  That can be a disadvantage; e.g. if the 5160 has an XT-class hard disk drive controller fitted (it has a ROM mapped C8000 to C9FFF).

Note too 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.