
Preliminary W77E516
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Wait State Control Signal
Either with the software using stretch value to change the required machine cycle of MOVX instruction,
the W77E516 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 (TA register) 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
MCycle
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
MCycle
SCycle
Wait-State
Cycle
Third
WAIT
sample
WAIT
sample WAIT
Extended duration
original rising edge
C2
C1
Fourth
Cycle