Rev.6.00 Oct.28.2004 page 239
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REJ09B0138-0600H
(b) Write Data Buffer Function and DMAC Operation Timing
The DMAC can start its next operation during external access using the write data buffer function. Consequently, the
DREQ
pin sampling timing,
TEND
output timing, etc., are different from the case in which the write data buffer function
is disabled. Also, internal bus cycles maybe hidden, and not visible.
(c) Write Data Buffer Function and
TEND
Output
A low level is not output from the
TEND
pin if the bus cycle in which a low level is to be output from the
TEND
pin is an
internal bus cycle, and an external write cycle is executed in parallel with this cycle. Note, for example, that a low level
may not be output from the
TEND
pin if the write data buffer function is used when data transfer is performed between an
internal I/O register and on-chip memory.
If at least one of the DMAC transfer addresses is an external address, a low level is output from the
TEND
pin.
Figure 7-42 shows an example in which a low level is not output at the
TEND
pin.
ø
Internal address
Internal read signal
External address
HWR
,
LWR
Internal write signal
TEND
Not output
DMA
read
External write by CPU, etc.
DMA
write
Figure 7-42 Example in Which Low Level is Not Output at
TEND
Pin
Activation by Falling Edge on
DREQ
Pin:
DREQ
pin falling edge detection is performed in synchronization with
DMAC internal operations. The operation is as follows:
[1] Activation request wait state: Waits for detection of a low level on the
DREQ
pin, and switches to [2].
[2] Transfer wait state: Waits for DMAC data transfer to become possible, and switches to [3].
[3] Activation request disabled state: Waits for detection of a high level on the
DREQ
pin, and switches to [1].
After DMAC transfer is enabled, a transition is made to [1]. Thus, initial activation after transfer is enabled is performed
by detection of a low level.
Activation Source Acceptance: At the start of activation source acceptance, a low level is detected in both
DREQ
pin
falling edge sensing and low level sensing. Similarly, in the case of an internal interrupt, the interrupt request is detected.
Therefore, a request is accepted from an internal interrupt or
DREQ
pin low level that occurs before execution of the
DMABCRL write to enable transfer.
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