w77e58 Winbond Electronics Corp America, w77e58 Datasheet - Page 44

• Manufacturer Part Number: w77e58
• Description: 8 Bit Microcontroller
• Manufacturer: Winbond Electronics Corp America

Wait State Control Signal
Either with the software using stretch value to change the required machine cycle of MOVX
instruction, the W77E58 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.
PORT 0
PORT 2
PSEN
CLK
ALE
WR
MOVX Inst.
C1
Address
of Previous
Last Cycle
Instruction
A0-A7
C2
A15-A8
C3
MOVX Inst.
C4
D0-D7
Figure 10. Data Memory Write with Stretch Value = 2
C1
Machine Cycle
Next Inst.
Address
A0-A7
C2
First
A15-A8
C3
Next Inst.
C4
Read
D0-D7
C1
MOVX Data
Machine Cycle
Address
A0-A7
C2
Second
- 44 -
MOVX instruction cycle
C3
C4
C1
Machine Cycle
C2
Third
A15-A8
C3
MOVX Data out
Preliminary W77E58
D0-D7
C4
C1
Machine Cycle
C2
Fourth
C3
C4
C1
Machine Cycle
Instruction
A0-A7
C2
Next
A15-A8
C3
C4
D0-D7