Motorola MVME2400 Series Manuale di Servizio Pagina 232

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3-46 Computer Group Literature Center Web Site
System Memory Controller (SMC)
3
possible after power-up reset so that SDRAM refresh
does not get behind. It is okay for the software then to take
some time to “up” CLK_FREQUENCY
to the correct
value. Refresh will get behind only when the actual CLK
pin’s frequency is lower than the value programmed into
CLK_FREQUENCY.
por por is set by the occurrence of power up reset. It is cleared
by writing a one to it. Writing a 0 to it has no effect.
ECC Control Register
refdis
When set, refdis causes the refresher and all of its
associated counters and state machines to be cleared and
maintained that way until refdis
is removed (cleared). If a
refresh cycle is in process when refdis
is updated by a
write to this register, the update does not take effect until
the refresh cycle has completed. This prevents the
generation of illegal cycles to the SDRAM when refdis
is
updated.
rwcb
rwcb, when set, causes reads and writes to SDRAM from
the PowerPC 60x bus to access check-bit data rather than
normal data. The data path used for reading and writing
check bits is D0-D7. Each 8-bit check-bit location
services 64 bits of normal data. The figure below shows
the relationship between normal data and check-bit data.
ADDRESS
$FEF80028
BIT
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
NAME
0
0
0
0
0
refdis
rwcb
derc
0
0
0
opien
scien
dpien
sien
mien
int
0
0
0
0
0
0
0
mbe_me
OPERATIO
N
R
R
R
R
R
R/W
R/W
R/W
R
R
R
R/W
R/W
R/W
R/W
R/W
R/C
READ ZERO
R
R
R
R
R
R
R
R/W
RESET
X
X
X
X
X
0 PL
0 PL
1 PL
X
X
X
0PL
0 PL
0 PL
0 PL
0PL
0PL
X
X
X
X
X
X
X
0 PL
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