3

Falcon ECC Memory Controller Chip Set

ram fref Some DRAMs require that they be refreshed at the rate of 7.8μs per row rather than the standard 15.6μs 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:

Table 3-11. ram spd1,ram spd0 and DRAM Type

ram spd0, ram spd1

DRAM Speed

DRAM Type

%00

70ns

Page Mode

%01

60ns

Page Mode

 

 

 

%10

-

Reserved

 

 

 

%11

50ns

EDO

 

 

 

 

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 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

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.

3-32

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Motorola MVME2300 Series manual Ram spd0,ram spd1, ram spd1,ram spd0 and Dram Type, Ram spd0, ram spd1 Dram Speed Dram Type