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SDRAM Controller Registers
7-8
élanSC520 Microcontroller Register Set Manual
Programming Notes
This register (DRCBENDADR) should be modified only when the write buffer and the read-ahead feature of the read
buffer are disabled in the DBCTL register (see page 8-3).
The value specified in each BNKx_END bit field determines the upper address boundary of the corresponding
SDRAM bank in 4Mbyte increments. Each bank’s lower boundary is determined by the end of the next-lower enabled
bank, so the addressable SDRAM space is the concatenation of the enabled banks. The top of the highest configured
bank is the top of memory.
If any particular bank is disabled (via its BNKx_ENB bit), the associated BNKx_END bit field value has no effect.
Banks do not have to be enabled contiguously. Figure 7-1 gives a few examples of SDRAM bank configuration.
Figure 7-1
Examples of Bank Ending Address Configuration
22
–
16
BNK2_END
[28
–
22]
Bank 2 Ending Address
This bit field determines the Bank 2 boundary, defined in 4-Mbyte increments. This value is
compared to physical address bits 28
–
22 during an SDRAM request to select a bank.
Bank 2 is selected if physical address bits 28–22 are less than the BNK2_END bit field value
but greater than or equal to the value specified by the BNK1_END bit field (or the next lower
enabled bank’s end value if Bank 1 is disabled.
15
BNK1_ENB
Bank 1 Enable
This bit enables Bank 1.
0 =Disabled
1 =Enabled
14
–
8
BNK1_END
[28
–
22]
Bank 1 Ending Address
This bit field determines the Bank 1 boundary, defined in 4-Mbyte increments. This value is
compared to physical address bits 28
–
22 during an SDRAM request to select a bank.
Bank 1 is selected if physical address bits 28–22 are less than the BNK1_END bit field value
but greater than or equal to the value specified by the BNK0_END bit field (or 0 if Bank 0 is
disabled).
7
BNK0_ENB
Bank 0 Enable
This bit enables Bank 0.
0 =Disabled
1 =Enabled
6
–
0
BNK0_END
[28
–
22]
Bank 0 Ending Address
This bit field determines the Bank 0 boundary, defined in 4-Mbyte increments. This value is
compared to physical address bits 28
–
22 during an SDRAM request to select a bank.
Bank 0 is selected if physical address bits 28–22 are less than the BNK0_END bit field value.
Bit
Name
Function
Bank 0
Bank 1
Bank 2
Bank 3
Example 1
Total
32 Mbytes
Example 2
56 Mbytes
Example 3
192 Mbytes
BNK0_END
= 02h
7FFFFFh
(8 Mbytes)
000000h
BNK1_END
= 04h
FFFFFFh
(8 Mbytes)
800000h
BNK2_END
= 06h
17FFFFFh
(8 Mbytes)
1000000h
BNK3_END
= 08h
1FFFFFFh
(8 Mbytes)
1800000h
BNK0_END
= 08h
1FFFFFFh
(32 Mbytes)
0000000h
BNK1_END
= 10h
3FFFFFFh
(32 Mbytes)
2000000h
BNK2_END
= 20h
7FFFFFFh
(64 Mbytes)
4000000h
BNK3_END
= 30h
BFFFFFFh
(64 Mbytes)
8000000h
BNK0_END
= 04h
FFFFFFh
(16 Mbytes)
000000h
BNK1_END
= 06h
17FFFFFh
(8 Mbytes)
1000000h
BNK2_END
= “Don’t Care”
Disabled
(BNK2_ENB = 0)
BNK3_END
= 0Eh
37FFFFFh
(32 Mbytes)
1800000h