
Preliminary W77IE58
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Figure 10. Data Memory Write with Stretch Value = 2
Wait State Control Signal
Either with the software using stretch value to change the required machine cycle of MOVX instruction,
the W77IE58 provides another hardware signal
WAIT
to implement the wider duration of external data
access timing. This wait state control signal is the alternate function of P4.0 such that it can only be
invoked to 44-pin PLCC/QFP package type. The wait state control signal can be enabled by setting WS
(ROMMAP.7) bit. When enabled, the setting of stretch value decides the minimum length of MOVX
instruction cycle and the device will sample the
WAIT
pin at each C3 state before the rising edge of
read/write strobe signal during MOVX instruction. Once this signal being recongnized, one more machine
cycle (wait state cycle) will be inserted into next cycle. The inserted wait state cycles are unlimited, so
the MOVX instruction cycle will end in which the wait state control signal is deactivated. Using wait state
control signal allows a dynamically access timimg to a selected external peripheral. The WS bit is
accessed by the Timed Access Protection procedure.
Wait State Control Signal Timing (when Stretch = 1)
C2 C3 C4
C1
CLOCK
ALE
PSEN
ADDRESS
RD / WR
C2 C3 C4
C1
C2 C3 C4
C1
C2 C3 C4
C1
C2 C3 C4
C1
MOVX Instruction
Cycle
SCycle
WCycle
Third
WAIT
sample
WAIT
sample WAIT
Extended duration
original rising edge
Wait State Control Signal Timing (when Stretch = 2)
C2 C3
C4
C1
CLOCK
ALE
PSEN
ADDRESS
RD / WR
C2 C3 C4
C1
C2 C3 C4
C1
C2 C3
C4
C1
C3 C4
C2
C1
MOVX Instruction
First
MCycle
SCycle
WCycle
Third
WAIT
sample
WAIT
sample WAIT
Extended duration
original rising edge
C2
C1
Fourth
Cycle