W77C58 Datasheet, PDF (39/71 Pages) Winbond – 8 BIT MICROCONTROLLER

Preliminary W77C58
Wait State Control Signal
Either with the software using stretch value to change the required machine cycle of MOVX
instruction, the W77C58 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
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
ALE
PSEN
ADDRESS
RD / WR
WAIT
original rising edge
Extended duration
sample
WAIT
sample WAIT
Wait State Control Signal Timing ( when Stretch = 2 )
CLOCK
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
ALE
PSEN
ADDRESS
RD / WR
WAIT
original rising edge
Extended duration
sample
WAIT
sample WAIT
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Publication Release Date: September 1999
Revision A1