3-34
Computer Group Literature Center Web Site
Falcon ECC Memory Controller Chip Set
3
ram fref Some DRAMs require that they be refreshed at the rate of 7.8
µ
s
per row rather than the standard 15.6
µ
s per row. If any of the DRAM
devices require the higher rate, then the ram fref bit should be left set,
otherwise, it can be cleared.
ram spd0,ram spd1 Together ram spd0,ram spd1 control DRAM
timing used by the Falcon pair. They are encoded as shown:
EDO refers to DRAMs that use an output latch on data. Sometimes these
parts are referred to as Hyper-Page Mode DRAMs.
To ensure reliable operation, the system should always be configured so
that these two bits are encoded to match the slowest devices that are used.
Also, if any parts do not support EDO, then these bits must set for Page
Mode. The only case in which it is permissible to set ram spd0,ram spd1
for 50ns, EDO is when all parts are 50ns and all support EDO.
chipu indicates which of the two positions within the Falcon pair is
occupied by this chip. When chipu is low, this chip is connected to the
lower half of the PowerPC 60x data bus and it does not drive TA_ or
AACK_. When chipu is high, this chip is connected to the upper half of
the PowerPC 60x data bus, and it drives TA_ and AACK_. chipu reflects
the level that was on the ERCS_ pin during power-up reset.
Table 3-12. ram spd1
,ram spd0 and DRAM Type
ram spd0, ram spd1
DRAM Speed
DRAM Type
%00
70ns
Fast Page
%01
60ns
Fast Page
%10
-
Reserved
%11
50ns
EDO