W78ERD2 Datasheet, PDF (51/72 Pages) Winbond – 8-BIT MICROCONTROLLER

W78ERD2
15. H/W REBOOT MODE (BOOT FROM LDROM)
By default, the W78ERD2 boots from AP Flash EPROM program after a power on reset. On some
occasions, user can force the W78ERD2 to boot from the LD Flash EPROM program via following
settings. The possible situation that you need to enter H/W REBOOT mode when the AP Flash
EPROM program can not run properly and device can not jump back to LD Flash EPROM to execute
in-system programming function. Then you can use this H/W REBOOT mode to force the W78ERD2
jumps to LD Flash EPROM and executes in-system programming procedure. When you design your
system, you may reserve the pins P2.6, P2.7 to switches or jumpers. For example in a CD-ROM
system, you can connect the P2.6 and P2.7 to PLAY and EJECT buttons on the panel. When the AP
Flash EPROM program fails to execute the normal application program. User can press both two
buttons at the same time and then turn on the power of the personal computer to force the W78ERD2
to enter the H/W REBOOT mode. After power on of personal computer, you can release both buttons
and finish the in-system programming procedure to update the AP Flash EPROM code. In application
system design, user must take care of the P2, P3, ALE, EA and PSEN pin value at reset to prevent
from accidentally activating the programming mode or H/W REBOOT mode.
H/W REBOOT MODE
P4.3
X
L
P2.7
L
X
P2.6
L
X
OPTION BIT
Bit4 = L
Bit5 = L
MODE
H/W REBOOT
H/W REBOOT
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Publication Release Date: April 20, 2005
Revision A4