W77IE58 Datasheet, PDF (48/90 Pages) Winbond – 8-BIT MICROCONTROLLER

Preliminary W77IE58
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)
CLOCK
ALE
PSEN
ADDRESS
RD / WR
WAIT
First
Machine
Cycle
Second
Machine
Cycle
Third
Machine
Cycle
MOVX Instruction
Wait-State
Cycle
C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4
original rising edge
Extended duration
sample
WAIT
sample WAIT
Wait State Control Signal Timing (when Stretch = 2)
CLOCK
ALE
PSEN
ADDRESS
RD / WR
WAIT
First
Machine
Cycle
Second
Machine
Cycle
Third
Machine
Cycle
MOVX Instruction
Fourth
Machine
Cycle
Wait-State
Cycle
C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4 C1 C2
original rising edge
Extended duration
sample
WAIT
sample WAIT
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