3

Falcon ECC Memory Controller Chip Set

Table 3-9. PowerPC 60x to ROM/Flash Address Mapping — ROM/Flash 64 Bits Wide (32 Bits per Falcon) (Continued)

PowerPC 60x A0-A31

ROM/Flash A22-A0

ROM/Flash Device Selected

 

 

 

$X3FFFFF9

$7FFFFF

Upper

 

 

 

$X3FFFFFA

$7FFFFF

Upper

 

 

 

$X3FFFFFB

$7FFFFF

Upper

 

 

 

$X3FFFFFC

$7FFFFF

Lower

 

 

 

$X3FFFFFD

$7FFFFF

Lower

 

 

 

$X3FFFFFE

$7FFFFF

Lower

 

 

 

$X3FFFFFF

$7FFFFF

Lower

 

 

 

Refresh/Scrub

The Refresh/Scrub operation varies according to 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 refreshes by doing a burst of four RAS_ cycles approximately once every 60μs. This increases to once every 30μs when certain DRAM devices are used. (The refresh rate is 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.

After each of the 4 cycles, the DRAM row address increments by one. When it reaches all 1s, it rolls over and starts anew at 0. Each time the row address rolls over, the block that is scrubbed toggles between A and B. Every second time that the row address rolls over, which of the 4 cycles that is a scrub changes from 1st to 2nd, from 2nd to 3rd, from 3rd to 4th, or from 4th to 1st. Every eighth time that the row address rolls over, the column address increments by one. When the column address reaches all ones, it rolls over and starts over at 0. Each time the column address rolls over, the SC1, SC0 bits in the scrub/refresh register increment by 1.

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Computer Group Literature Center Web Site

Page 180
Image 180
Motorola MVME2300 Series manual Refresh/Scrub, Blocks a and/or B Present, Blocks C and D Not Present