Datasheet

2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
DRAM Controller
11-14 MCF5206e USER’S MANUAL MOTOROLA
From a hardware point of view, a smaller DRAM is simply not connected to the upper
address pins. When a larger DRAM is installed, all address pins are connected. From a
software point of view, the DRAMC Mask Register (DCMR) contents are modified to mask
more of the address bits for the larger DRAM. The bank page size (BPS) in the DRAMC
Control Register (DCCR) must remain the same, even if the larger DRAM can support a
larger page size. If the BPS field is changed, the address multiplexing also changes—
requiring a different printed circuit board layout.
For example, suppose the system DRAM is 8 bits wide and can range from 1 MByte (1 M
x 8 bits) to 4 MBytes (4 M x 8 bits), with a page size of 1 KByte. Referring to Table 11-8,
address pins A[10:19] and A[21] should be routed to the DRAM socket pins. For the 4 M
x 8 DRAM, the MCF5206e address pins A[10:19] and A[21] are connected to the DRAM
address inputs A[0:10] (see Figure 11-3). For the 1 M x 8 DRAM, the MCF5206e address
pins A[10:19] are connected to the DRAM address inputs A[0:9] (see Figure 11-4).
Because the address connections for the 1 M x 8 are a subset of those for the 4 M x 8,
the address multiplexing scheme allows a system using the MCF5206e to upgrade the
memory size without requiring different printed circuit board layouts. The only required
change is the number of bits masked in the DCMR.
It should be noted that the page size, in this example, is determined by the 1 M x 8 DRAM
(9 column address bits gives a page size of 1 KByte), and that even though the 4 M x 8
DRAM could support a 2 KByte page size, the page size must be programmed to 1 KByte
to keep the address multiplexing the same.
Table 11-9. Bank Page Size Versus Actual DRAM Page Size
BANK PAGE SIZE
(BPS)
PORT SIZE PAGE ADDRESS
ACTUAL DRAM
PAGE SIZE
512 Bytes
8 bits A[8:0] 512 Bytes
16 bits A[8:1] 256 Bytes
32 bits A[8:2] 128 Bytes
1 KByte s
8 bits A[9:0] 1 KBytes
16 bits A[9:1] 512 Bytes
32 bits A[9:2] 256 Bytes
2 KBytes
8 bits A[10:0] 2 KBytes
16 bits A[10:1] 1 KBytes
32 bits A[10:2] 512 Bytes
Fr
eescale S
emiconduct
or
, I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
nc...