W77LE516 Datasheet, PDF (40/89 Pages) Winbond – 8-BIT MICROCONTROLLER

W77LE516/W77L516A
CLK
ALE
PSEN
WR
PORT 0
Last Cycle
of Previous
Instruction
First
Machine Cycle
Second
Machine Cycle
Third
Machine Cycle
Fourth
Next
Machine Cycle ^Instruction
Machine Cycle
MOVX instruction cycle
C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4 C1 C2 C3 C4
A0-A7
D0-D7 A0-A7
D0-D7 A0-A7
D0-D7
A0-A7
D0-D7
PORT 2
MOVX Inst.
Address
Next Inst.
Address
MOVX Data
Address
MOVX Inst.
Next Inst.
Read
A15-A8
A15-A8
MOVX Data out
A15-A8
A15-A8
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 W77L516A 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 (WSCON.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
recognized, 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 timing to a selected
external peripheral. The WS bit is accessed by the Timed Access Protection procedure.
Set WS bit and stretch value = 0 to enable wait signal.
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