Chapter 3 - Installing Instrument Boards
77
If a board needs to use more than 32 addresses, then the switch
A5 would also need to be disabled using A5EN switch, thus
allowing the maximum of 64 internal addresses for one board.
In a similar manner, A5EN, A10EN, A11EN, and A12EN have
the same meaning for more offset address choices.
Enabling switch
Offset address
increments
A10EN 0x400H
A11EN 0x800H
A12EN 0x1000H
Table 3-14: A10EN through A12EN offset addresses
For example, a board uses the addresses 300H, 301H, 700H,
and 701H. Since the last two addresses are over 400H, in order
to be able to code 700H–701H, A10EN must be set to OFF.
The default settings for the addresses masks are:
A4EN
ON
Board uses no more then.
A5EN
ON
16 consecutive addresses
A10EN OFF
A11EN
OFF
Offset address increments of 1000H.
A12EN ON
Table 3-15: A4EN through A12EN Default Settings
4. Set the special addressing modes (optional).
The 702EN switch is used to disable the base address decoding.
This, combined with the PnPEN switch, is useful when
configuring plug-and-play (PnP) ISA boards. When a PnP
board is first powered up, it is not assigned a base address. The
CPU communicates with the board using the 0x274-0x27B
address range, which is enabled with the PnPEN switch. (See
Configuring Plug-and-Play Boards later in this chapter)
The 16BitEN switch is used to decrease delay of CS16 signals.
When this switch is in the ‘On’ position, and the set address
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