Motorola ColdFire MCF5281 - Manual (Page 221)

Chip Select Module
Freescale Semiconductor 12-7
12.4.1.3 Chip Select Control Registers (CSCR0–CSCR6)
Each CSCR, shown in Figure 12-4 , controls the auto-acknowledge, port size, burst capability, and
activation of each chip select. Note that to support the external boot chip select, CS0, the CSCR0 reset
values differ from the other CSCRs. CS0 allows address decoding for boot ROM before system
initialization.
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] = 0x0001, 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.
5–1 C/I,
SC,
SD,
UC, UD
Address space mask bits. These bits determine whether the specified accesses can occur to the address
space defined by the BAM for this chip select.
C/I
CPU space and interrupt acknowledge cycle mask
SC Supervisor code address space mask
SD Supervisor data address space mask
UC User code address space mask
UD User data address space mask
0 The address space assigned to this chip select is available to the specified access type.
1 The address space assigned to this chip select is not available (masked) to the specified access type.
If this address space is accessed, chip select is not activated and a regular external bus cycle occurs.
Note that if AM = 0, SC, SD, UC, and UD are ignored in the chip select decode on DMA access.
0 V Valid bit. Indicates whether the corresponding CSAR, CSMR, and CSCR contents are valid. Programmed
chip selects do not assert until V is set (except for CS0, which acts as the global chip select). Reset clears
each CSMRn[V].
0 Chip select invalid
1 Chip select valid
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3