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3-22
Computer Group Literature Center Web Site
Falcon ECC Memory Controller Chip Set
3
Refresh/Scrub
Refresh/Scrub is done differently based on which DRAM blocks are
populated: (A and/or B) but not (C and D), or (A and/or B) and (C and/or
D).
Blocks A and/or B Present, Blocks C and D Not Present
The Falcon pair performs refresh by doing a burst of four RAS_ cycles
approximately once every 60
µ
s. This increases to once every 30
µ
s when
certain DRAM devices are used. (Controlled by the ram_fref bit in the
status registers.) RAS_ is asserted to both of Blocks A and B during each
of the 4 cycles. Along with RAS_, the Falcon pair also asserts CAS_ with
(OE_ then WE_) to one of the blocks during one of the four cycles. This
forms a read-modify-write which is a scrub cycle to that location.
$X3FFFFF2
$7FFFFE
Upper
$X3FFFFF3
$7FFFFE
Upper
$X3FFFFF4
$7FFFFE
Lower
$X3FFFFF5
$7FFFFE
Lower
$X3FFFFF6
$7FFFFE
Lower
$X3FFFFF7
$7FFFFE
Lower
$X3FFFFF8
$7FFFFF
Upper
$X3FFFFF9
$7FFFFF
Upper
$X3FFFFFA
$7FFFFF
Upper
$X3FFFFFB
$7FFFFF
Upper
$X3FFFFFC
$7FFFFF
Lower
$X3FFFFFD
$7FFFFF
Lower
$X3FFFFFE
$7FFFFF
Lower
$X3FFFFFF
$7FFFFF
Lower
Table 3-10. PowerPC 60x to ROM/Flash Address Mapping when ROM/Flash
is 64 Bits Wide (32 Bits per Falcon) (Continued)
PowerPC 60x A0-A31
ROM/Flash A22-A0
ROM/Flash Selected