Chapter 3 - Installing Instrument Boards
67
A9 A8 A7 A6 A5 A4 A3 A2 A1 A0
1 0
1 0 1 0
0
0
0
0
2. Set the offset address.
If two boards have the same value for A9-A4 in their base
address, say 300H (11,0000,0000)
A9 A8 A7 A6 A5 A4 A3 A2 A1 A0
1 1
0 0 0 0
0
0
0
0
and 308H (11,0000,1000),
A9 A8 A7 A6 A5 A4 A3 A2 A1 A0
1 1
0 0 0 0
1
0
0
0
then they must use different offset addresses, so their switch
settings will be unique.
The default offset address is zero.
Note:
Some instrument boards’ software drivers do not accept
addresses greater than 3FFH. If this is the case, an
offset address of 0000H should be used.
3. Set the address mask (optional).
An A4EN address mask is used to allow ignoring the A4
switch, so a larger address range can be accessed. With A4EN
(on), every setting of one offset and base address uses sixteen
addresses (A0 through A3).
For example, if a board uses a range of addresses for I/O, say
the 20 addresses from 300H to 313H, then the addresses in the
range of 300H through 30FH have A4=0 (up to sixteen
addresses). The addresses in the range of 310H to 313H, would
have A4 = 1 (for more than sixteen addresses up to 32). To
enable A4 to be used for more than sixteen addresses, it is
necessary to turn A4EN = OFF.
If a board needs to use more than 32 addresses, then the switch
A5 also needs to be disabled. Since the GT7020 does not have
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