Microcontroller User's Manual

MOTOROLA Chapter 12. Chip Select Module 12-7
Chip Select Registers
12.4.1.2 Chip Select Mask Registers (CSMR0–CSMR6)
The CSMRs, Figure 12-3, are used to specify the address mask and allowable access types
for the respective chip selects.
.
Table 12-7 describes CSMR fields.
Table 12-6. CSARn Field Description
Bits Name Description
15–0 BA Base address. Defines the base address for memory dedicated to chip select CS[6:0]. BA is compared
to bits 31–16 on the internal address bus to determine if chip select memory is being accessed.
31 1615 9876543210
Field BAM — WP — AM C/I SC SD UC UD V
Reset Unitialized 0
R/W R/W
Addr 0x084 (CSMR0); 0x090 (CSMR1); 0x09C (CSMR2); 0x0A8 (CSMR3);
0x0B4 (CSMR4); 0x0C0 (CSMR5); 0x0CC (CSMR6)
Figure 12-3. Chip Select Mask Registers (CSMRn)
Table 12-7. CSMRn Field Descriptions
Bits Name Description
31–16 BAM Base address mask. Defines the chip select block by masking address bits. Setting a BAM bit causes
the corresponding CSAR bit to be ignored in the decode.
0 Corresponding address bit is used in chip select decode.
1 Corresponding address bit is a don’t care in chip select decode.
The block size for CS
[6:0] is 2
n
where n = (number of bits set in respective CSMR[BAM]) + 16.
So, if CSAR0 = 0x0000 and CSMR0[BAM] = 0x0008, CS0
addresses a 128-Kbyte (2
17
byte) range
from 0x0000–0x1_FFFF.
Likewise, for CS0 to access 32 Mbytes (2
25
bytes) of address space starting at location 0x0000, and
for CS1
to access 16 Mbytes (2
24
bytes) of address space starting after the CS0 space, then CSAR0
= 0x0000, CSMR0[BAM] = 0x01FF, CSAR1 = 0x0200, and CSMR1[BAM] = 0x00FF.
8 WP Write protect. Controls write accesses to the address range in the corresponding CSAR. Attempting
to write to the range of addresses for which CSARn[WP] = 1 results in the appropriate chip select
not being selected. No exception occurs.
0 Both read and write accesses are allowed.
1 Only read accesses are allowed.
7 — Reserved, should be cleared.
6 AM Alternate master. When AM = 0 during a DMA access, SC, SD, UC, and UD are don’t cares in the
chip select decode.