Chip-Select Operation
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 17-9

17.5.2.2 Chip-Select Mask Registers (CSMR0–CSMR5)

CSMRn, Figure 17-4, are used to specify the address mask and allowable access types for the respective

chip-selects.

Table 17-8 describes CSMR fields.

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
R BAM
W
Reset0000000000000000
1514131211109876543210
R0000000WP0000000V
W
Reset0000000000000000
Reg
Addr
MBAR + 0x504 (CSMR0); 0x510 (CSMR1); 0x51C (CSMR2);
0x528 (CSMR3); 0x534 (CSMR4); 0xr540 (CSMR5)

Figure 17-4. Chip-Select Mask Registers (CSMRn)

Table 17-8. CSMRn Field Descriptions

Bits Name Description
31–16 BAM Base address mask. Defines the chip-select block size by masking address bits. Setting a BAM bit
causes the corresponding CSAR bit to be a “don’t care” 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 FBCSn is 2n; n = (number of bits set in respective CSMR[BAM]) + 16.
For example, if CSAR0 = 0x0000 and CSMR0[BAM] = 0x0008, FBCS0 would address two
discontinuous 64-Kbyte memory blocks: one from 0x0000–0xFFFF and one from
0x8_0000–0x8_FFFF.
Likewise, for FBCS0 to access 32 Mbytes of address space starting at location 0x0, FBCS1 must
begin at the next byte after FBCS0 for a 16-Mbyte address space. Then CSAR0 = 0x0000,
CSMR0[BAM] = 0x01FF, CSAR1 = 0x0200, and CSMR1[BAM] = 0x00FF.
15–9 Reserved, should be cleared
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
7–1 Reserved, should be cleared
0 V Valid bit. Indicates whether the corresponding CSAR, CSMR, and CSCR contents are valid.
Programmed chip-selects do not assert until V bit is set (except for FBCS0, which acts as the global
chip-select). Reset clears each CSMRn[V]. At reset, no chip-select other than FBCS0 can be used
until the CSMR0[V] is set. At which point FBCS[5:0] functions as configured.
0 chip-select invalid
1 chip-select valid