Motorola DigitalDNA ColdFire MCF5272 User Manual page 461

Table 20-4. Data Bus Requirement for Read Cycles
Transfer Size A[1:0]
Byte
Word
Longword
Line
Table 20-5 lists the transfer size, A[1:0], and the corresponding pattern of the data transfer
for write cycles from the internal multiplexer of the MCF5272 to the external data bus. For
example, if a longword transfer is generated to a 16-bit port, the MCF5272 starts the cycle
with A[1:0] set to 0x0 and reads the first word. The address in then incremented to 0x2 and
the second word is read. The data for both word reads is taken from D[31:16]. Bytes labeled
"X" are don't cares.I
Table 20-5. Internal to External Data Bus Multiplexer–Write Cycle
32-Bit Port
D[31:24] D[23:16] D[15:8]
00 Byte 0 X
01 X Byte 1
10 X X
11 X X
00 Byte 0 Byte 1
01 — —
10 X X
11 — —
00 Byte 0 Byte 1
01 — —
10 — —
11 — —
00 Byte 0 Byte 1
01 — —
10 — —
11 — —
Transfer Size A[1:0]
D[31:24] D[23:16] D[15:8] D[7:0]
Byte 00
01
10
11
Word 00
01
10
11
Chapter 20. Bus Operation
External Data Bytes Required
16-Bit Port
D[7:0] D[31:24] D[23:16]
X X Byte 0
X X X
Byte 2 X Byte 2
X Byte 3 X
X X Byte 0
— — —
Byte2 Byte 3 Byte 2
— — —
Byte 2 Byte 3 Byte 0
— — —
— — Byte 2
— — —
Byte 2 Byte 3 Byte 0
— — —
— — Byte 2
— — —
External Data Bus Connection
OP3 X X
OP3 OP3 X
OP3 X OP3
OP3 OP3 X
OP2 OP3 X
OP3 X X
OP2 OP3 OP2
OP3 X X
Data Transfer Mechanism
8-Bit Port
D[31:24]
X Byte 0
Byte 1 Byte 1
X Byte 2
Byte 3 Byte 3
Byte 1 Byte 0
— Byte 1
Byte 3 Byte 2
— Byte 3
Byte 1 Byte 0
— Byte 1
Byte 3 Byte 2
— Byte 3
Byte 1 Byte 0
— Byte 1
Byte 3 Byte 2
— Byte 3
X
X
X
OP3
X
X
OP3
X
20-9