14-24
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part IV. Hardware Interface
The MPC860 transfers operands through its 32-bit data port. If the transfer is controlled by
the internal memory controller, the MPC860 can support 8- and 16-bit data port sizes. The
bus requires that the portion of the data bus used for a transfer to or from a particular port
size be Þxed. A 32-bit port must reside on D[0Ð31], a 16-bit port must reside on D[0Ð15],
and an 8-bit port must reside on D[0Ð7]. The MPC860 always tries to transfer the maximum
amount of data on all bus cycles; for a word operation, it always assumes that the port is 32
bits wide when beginning the cycle. Figure 14-19, Figure 14-20, Table 14-2, and
Table 14-3 use the following conventions:
¥
OP0 is the MSB of a word operand; OP3 is the LSB.
¥
The two bytes of a half-word operand are OP0 (most-signiÞcant) and OP1 or OP2
(most-signiÞcant) and OP3, depending on the address of the access.
¥
The single byte of a byte-length operand is OP0, OP1, OP2, or OP3, depending on
the address of the access.
Figure 14-19. Internal Operand Representation
Figure 14-20 shows the device connections on the data bus.
Figure 14-20. Interface to Different Port Size Devices
OP0
OP1
OP2
OP3
Word
OP0
OP1
OP2
OP3
OP0
OP1
OP2
OP3
Half Word
Byte
0
31
OP0
OP1
OP2
OP3
16-Bit Port Size
OP0
OP1
OP2
OP3
Interface Output
0
31
D[0Ð7]
D[8Ð15]
D[16Ð23]
D[24Ð31]
OP0
OP1
OP2
OP3
32-Bit Port Size
OP0
OP1
8-Bit Port Size
OP2
OP3
Register
Содержание MPC860 PowerQUICC
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