138
8.4.2
Wait State Control
The number of external memory space access states and the insertion of wait states can be
controlled using the WCR1–WCR3 bits. The bus cycles that can be controlled are the CPU read
cycle and the DMAC dual mode read cycle. The bus cycle that can be controlled using the WCR2
is the DMAC single-mode read/write cycle.
Table 8.9 shows the number of states and number of wait states in access cycles to external
memory spaces.
Table 8.9
Number of States and Number of Wait States in Access Cycles to External
Memory Spaces
CPU Read Cycle, DMAC Dual Mode Read Cycle,
DMAC Single Mode Read/Write Cycle
Area
Corresponding Bits in
WCR1 and WCR2 = 0
Corresponding Bits in
WCR1 and WCR2 = 1
1, 3–5, 7
1 cycle fixed;
WAIT
signal ignored
2 cycles fixed + wait state from
WAIT
signal
*
3
0, 2, 6 (long
wait available)
1 cycle + long wait state,
WAIT
signal ignored
1 cycle + long wait state
*
1
+ wait state from
WAIT
signal
Notes:
*
1 The number of long wait states is set by WCR3.
*
2 When DRAME = 1, short pitch/long pitch is selected with the WW1 bit in WCR1.
*
3 Pin wait cannot be used for the CS7 and
WAIT
pins of area 3 because they are
multiplexed.
For the CPU read cycle, DMAC dual mode read cycle, and DMAC single mode read/write cycle,
the access cycle is completed in 1 state when the corresponding bits of WCR1 and WCR2 for
areas 1, 3–5, and 7 are cleared to 0 and the
WAIT
pin input signal is not sampled. When the bits
are set to 1, the
WAIT
signal is sampled and the number of states is 2 plus the number of wait
states set by the
WAIT
signal. The
WAIT
signal is sampled at the rise of the system clock (CK)
directly preceding the second state of the bus cycle and the wait states are inserted as long as the
level is low. When a high level is detected, it shifts to the second state (final state). Figure 8.13
shows the wait state timing when accessing the external memory spaces of areas 1, 3, 4, 5, and 7.
CPU Write Cycle and
DMAC Dual Mode Write
Cycle (Cannot be
controlled by WCR1)
*
2
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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