Section 9 16-Bit Timer Pulse Unit (TPU)
Rev. 3.00 Mar. 14, 2006 Page 336 of 804
REJ09B0104-0300
(4)
Status Flag Clearing Timing
After a status flag is read as 1 by the CPU, it is cleared by writing 0 to it. When the DMAC is
activated, the flag is cleared automatically. Figure 9.43 shows the timing for status flag clearing by
the CPU, and figure 9.44 shows the timing for status flag clearing by the DMAC.
Status flag
P
φ
Interrupt request
signal
Address
Write
T1
T2
TSR address
TSR write cycle
Figure 9.43 Timing for Status Flag Clearing by CPU
The status flag and interrupt request signal are cleared in synchronization with P
φ
after the DMAC
transfer has started, as shown in figure 9.44. If conflict occurs for clearing the status flag and
interrupt request signal due to activation of multiple DMAC transfers, it will take up to five clock
cycles (P
φ
) for clearing them, as shown in figure 9.45. The next transfer request is masked for a
longer period of either a period until the current transfer ends or a period for five clock cycles (P
φ
)
from the beginning of the transfer.
P
φ
Address
Status flag
Interrupt request
signal
Source
address
Destination
address
Period in which the next transfer request is masked
T1
T2
DMAC
read cycle
DMAC
write cycle
T1
T2
Figure 9.44 Timing for Status Flag Clearing by DMAC Activation (1)
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