2-12
VL-1225/6 Analog Input/Output Board
MEMEX Signal
The MEMEX (memory expansion) signal on the STD Bus is normally used to select between two different
memory banks or maps. It can be used to double the number of available memory addresses in the system
(by selecting between the two memory banks). The MEMEX signal is usually controlled by (or jumpered
to ground on) the system CPU card.
A low MEMEX signal usually selects the standard or normal memory map. A high MEMEX signal usually
selects the secondary or alternate memory map. Boards that ignore (or do not decode) MEMEX will appear
in both memory maps.
As shipped the MEMEX jumper is configured to ignore the MEMEX signal. The board will be addressed
whether the MEMEX signal is high or low. It can be jumpered for two other modes as shown below.
Jumper
Jumper
Jumper
Jumper
Jumper
As
As
As
As
As
Block
Block
Block
Block
Block
Description
Description
Description
Description
Description
Shipped
Shipped
Shipped
Shipped
Shipped
V8
MEMEX Select . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ignore
V8
1-2
= In,
V8
2-3
= Out
– Ignore MEMEX
V8
1-2
= Out,
V8
2-3
= Out
– Enable on MEMEX high
V8
1-2
= Out,
V8
2-3
= In
– Enable on MEMEX low
Figure 2-10. MEMEX Options
Configuration – Board Addressing
