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Revision C system board
I/O registers
The function of two of the Apricot specific I/O ports are different on the revision C
system board. The two ports are 121h and 12Ch.
On revision C of the system board, port 121h is used to control the diagnostic LED
on the system board. When bit 0 of this port is low (default) the diagnostic LED is lit.
when it is set high the diagnostic LED is extinguished.
Bits 4 and 5 of port 12Ch are reserved on revision C system boards. 12Ch is used only
to control the microphone level.
System memory
Revision C systems may have 2 or 4 Mbytes of RAM soldered to the system board and
provide an additional option ROM socket.
When 4 Mbytes of RAM is installed during manufacture four SIMM sockets are fitted.
When 2 Mbytes of RAM is installed six SIMM sockets are fitted.
SIMMs must be installed in pairs, upgrades of 2 and 8 Mbytes are available. The 2 Mbyte
upgrade contains two 60nS 1Mx9 SIMMs, the 8 Mbyte upgrade contains two 60nS
4Mx9 SIMMs.
The following table identifies the valid upgrade combinations.
System board
capacity (Mbytes)
Notes
1. For both system board RAM capacities an alternative method of achieving 8 Mbytes
of RAM is to install an 8 Mbyte upgrade in bank 2 and leave the other bank (or banks)
empty. This configuration disables the RAM soldered to the system board.
2. When banks 2 and 3 are both occupied by 8 Mbyte upgrades the RAM soldered to the
system board is disabled.
B/4 LS PRO HARDWARE TECHNICAL REFERENCE
Upgrade
to (Mbytes)
2
4
2
6
2
8
2
12
2
16
4
6
4
8
4
12
4
16
Bank
1
2
3
2
-
-
2
2
-
2
2
2
2
8
-
-
8
8
N/A
2
-
N/A
2
2
N/A
8
-
N/A
8
8
Note
1
2
1
2
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