Datasheet

Chapter 18. Bus Operation 18-11
Data Transfer Operation
Figure 18-11. Back-to-Back Bus Cycles
Basic read and write cycles are used to show a back-to-back cycle, but there is no restriction
as to the type of operations to be placed back to back. The initiation of a back-to-back cycle
is not user definable.
18.4.7 Burst Cycles
The MCF5407 can be programmed to initiate burst cycles if its transfer size exceeds the
size of the port it is transferring to. For example, with bursting enabled, a word transfer to
an 8-bit port would take a 2-byte burst cycle for which SIZ[1:0] = 10 throughout. A line
transfer to a 32-bit port would take a 4-longword burst cycle, for which SIZ[1:0] = 11
throughout.
The MCF5407 bus can support 2-1-1-1 burst cycles to maximize cache performance and
optimize DMA transfers. A user can add wait states by delaying termination of the cycle.
The initiation of a burst cycle is encoded on the size pins. For burst transfers to smaller port
sizes, SIZ[1:0] indicates the size of the entire transfer. For example, if the MCF5407 writes
a longword to an 8-bit port, SIZ[1:0] = 00 for the first byte transfer and does not change.
CSCRs are used to enable bursting for reads, writes, or both. MCF5407 memory space can
be declared burst-inhibited for reads and writes by clearing the appropriate
CSCRx[BSTR,BSTW]. A line access to a burst-inhibited region is broken into separate
port-width accesses. Unlike a burst access, SIZ[1:0] = 11 only for the first port-width
access; for the remaining accesses, SIZ[1:0] reflects the port width, with individual
accesses separated by AS
negations. The address changes if internal termination is used but
does not change if external termination is used, as shown in Figure 18-12 and Figure 18-14.
A[31:0], TT[1:0]
R/W
TIP
TS
AS, CSx
D[31:0]
TA
Read
S0 S1 S2 S3 S4 S5
S0 S1 S2 S3 S4 S5
Write
OE
CLKIN
BE
/BWEx
TM[2:0], SIZ[1:0]