MOTOROLA
MC68349 USER'S MANUAL
4- 35
4.3.4.2 ADDRESS MASK REGISTERS. There are four 32-bit address mask registers in
the chip select function, one for each chip select signal.
Address Mask
$040 (CS0), $048 (CS1), $050 (CS2), $058 (CS3)
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
AM31
AM30
AM29
AM28
AM27
AM26
AM25
AM24
AM23
AM22
AM21
AM20
AM19
AM18
AM17
AM16
RESET:
UUUUUUUUUUUUUUUU
15
14
13
12
11
10
9876543210
AM15
AM14
AM13
AM12
AM11
AM10
AM9
AM8
FCM3
FCM2
FCM1
FCM0
DD1
DD0
PS1
PS0
RESET:
UUUUUUUUUUUUUUUU
U = Unaffected by reset
Supervisor Only
AM31–AM8—Address Mask Bits 31–8
The address mask field, the upper 24 bits of each address mask register, defines the
chip select block size. The block size is equal to 2n, where n = (number of bits set in the
address mask field) + 8.
Any set bit masks the corresponding base address register bit (the base address
register bit becomes a don’t care). By masking the address bits independently, external
devices of different size address ranges can be used. Address mask bits can be set or
cleared in any order in the field, allowing a resource to reside in more than one area of
the address map. This field can be read or written at any time.
FCM3–FCM0—Function Code Mask Bits 3–0
This field can be used to mask certain function code bits, allowing more than one
address space type to be assigned to a chip select. Any set bit masks the
corresponding function code bit.
DD1, DD0—DSACK Delay Bits 1 and 0
This field, along with the EDS bit of the corresponding base address register,
determines the number of wait states added before an internal DSACK≈ is returned for
that entry. Table 4-11 lists the encoding for the EDS and DDx bits.
NOTE
The port size field must be programmed for an internal
DSACK≈ response and the EDS and DDx bits to have
significance. If external DSACK≈ signals are returned earlier
than indicated by the EDS and DDx bits, the cycle will
terminate sooner than programmed. See 4.2.5.2 PORT B for a
discussion on using the internal DSACK≈ generation without
using the CS≈ signal.