Datasheet

Bus Operation
MOTOROLA MCF5206e USER’S MANUAL 6-9
The MCF5206e can burst anytime the port size of the external slave being accessed is
smaller than the operand size. If bursting is enabled, the MCF5206e performs burst
transfers depending on the port size and operand alignment. For any transfer, the number
of bytes transferred during a bus cycle is equal to or less than the size indicated by the
SIZx outputs. For example, during the first bus cycle of a longword transfer to a 16-bit port
where bursting is enabled, the SIZx outputs remains constant throughout the transfer and
indicates that four bytes are to be transferred, although only two bytes are moved at a
time.Table 6-5 lists the encodings for the SIZx bits for each port size for transfers where
bursting is both enabled and disabled.
A[0] and A[1] also affect operation of the data multiplexer. During an operand transfer,
A[31:2] indicate the longword base address of that portion of the operand to be accessed;
A[1] and A[0] indicate the byte offset from the base. Table 6-6 lists the encoding of A[1]
and A[0] and the corresponding byte offset from the longword base.
Table 6-7 lists the bytes that should be driven on the data bus during read cycles by the
slave device being accessed. The entries shown as Byte X are portions of the requested
operand that are read. The operand being read is defined by SIZ[1], SIZ[0], A[0], and A[1]
for the bus cycle. Bytes labeled X are “don’t cares” and are not required during that read
cycle. Bytes labeled “-” indicates that this transfer is not valid.
Table 6-5. SIZx Encoding for Burst- and Bursting-Inhibited Ports
OPERAND
SIZE
32-BIT PORT 16 -BIT PORT 8-BIT PORT
BURSTING
ENABLED
BURSTING
INHIBITED
BURSTING
ENABLED
BURSTING
INHIBITED
BURSTING
ENABLED
BURSTING
INHIBITED
SIZ[1] SIZ[0] SIZ[1] SIZ[0] SIZ[1] SIZ[0] SIZ[1] SIZ[0] SIZ[1] SIZ[0] SIZ[1] SIZ[0]
BYTE 010101010101
WORD101010101001
LONGWORD000000100001
LINE 110011101101
Table 6-6. Address Offset Encoding
A[1] A[0] OFFSET
0 0 +0 Byte
0 1 +1 Byte
1 0 +2 Bytes
1 1 +3 Bytes
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