MPC563XM Reference Manual, Rev. 1
Freescale Semiconductor
395
Preliminary—Subject to Change Without Notice
13.5.2.14 Address Data Multiplexing
Address/Data multiplexing enables the design of a system with reduced pin count. In such a system,
multiplexed address/data functions (on DATA pins) are used, instead of having separate address and data
pins. Compared to the normal EBI specification (e.g. 24 address pins+32 data pins), only 32 data pins are
required. Compared to a 16-bit bus implementation, only 24 pins are required (e.g. ADDR[8:15] +
ADDR[16:31]/DATA[16:31]).
When performing a small access read, as described in
Section 13.5.2.6, “Small Accesses (Small Port Size
, with A/D multiplexing enabled for this access, the EBI inserts an idle clock cycle
with OE negated and CS asserted, to allow for the memory to three-state the bus prior to the EBI driving
the address on the next clock. This clock gap already exists (for other reasons) for non-small-access
transfers, so no additional clock gap is inserted for those cases. See
for an example of a small
access read with A/D multiplexing enabled.
4
0
Half @0x3
(2 AHB
transfers)
11
6
1110
-
z00
0111
4
1
11
1011
-
z00
0111
8
0
Word @0x1
(2 AHB
transfers)
00
1000
-
z00
0111
8
1
00
10
1011
0011
-
z00
0111
9
0
Word @0x2
(2 AHB
transfers)
00
1100
-
z00
0011
9
1
10
0011
-
z00
0011
10
0
Word @0x3
(2 AHB
transfers)
11
1110
11
z00
0001
10
1
11
1011
11
z00
z10
0011
0111
1
Misaligned case number, from
.
2
Port size; 0=32 bits, 1=16 bits.
3
External ADDR pins, not necessarily the address on internal master
AHB bus.
4
For address with Z - address bit 29 will increment to next word. For
all other cases, address bit 29 will be unchanged.
5
External WE_BE pins. Note that these pins have negative polarity,
opposite of the internal byte strobes in
.
6
Treated as 1-byte access.
Table 13-26. Misalignment Cases Supported by a 32 bit AMBA EBI (external bus) (continued)
#
1
PS
2
Program Size
and byte offset
ADDR[30:31]
3,4
WE_BE[0:3]
5