205
•
DREQ
pin sampling timing in cycle-steal mode
In cycle-steal mode, the sampling timing is the same regardless of whether
DREQ
is detected
by edge or level. With edge detection, however, once the signal is sampled it will not be
sampled again until the next edge detection. Once
DREQ
input is detected, the next sampling
is not performed until the first state, among those DMAC bus cycles thereby produced, in
which a DACK signal is output (including the detection state itself). The next sampling occurs
immediately prior to the rising edge of the clock pulse (CK) of the third state after the bus
cycle previous to the bus cycle in which the DACK signal is output.
Figures 9.13 to 9.22 show the sampling timing of the
DREQ
pin in cycle-steal mode for each
bus cycle. When no
DREQ
input is detected at the sampling after the aforementioned
DREQ
detection, the next sampling occurs in the next state in which a DACK signal is output. If no
DREQ
input is detected at this time, sampling occurs at every subsequent state.
CK
DREQ
DACK
Bus cycle
CPU
CPU
CPU
DMAC
CPU
CPU
CPU
CPU
Figure 9.13
DREQ
Sampling Timing in Cycle-Steal Mode (Output with
DREQ
Level
Detection and DACK Active-Low) (Single Address Mode, Bus Cycle = 1 State)
Summary of Contents for HD6417032
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Page 525: ...490 CK RAS CAS TRp TRc TRcc tRASD1 tRASD2 tCASD3 tCASD2 TRr tCSR Figure 20 18 Self Refresh ...
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