W79E548 Datasheet, PDF (62/79 Pages) Winbond – 8-BIT MICROCONTROLLER

W79E548/W79L548
14. H/W REBOOT MODE (BOOT FROM 4K BYTES OF LDFLASH)
The W79E(L)548 boots from APFlash program (64K bytes) by default at the external reset. On some
occasions, user can force W79E(L)548 to boot from the LDFlash program (4K bytes) at the external
reset. The settings for this special mode is as follow. It is necessary to add 10K resistor on these P2.6,
P2.7 and P4.3 pins.
Reboot Mode
OPTION BITS
Bit4 L
Bit5 L
RST
P4.3
P2.7
H
X
L
H
L
X
P2.6
L
X
MODE
REBOOT
REBOOT
The Reset Timing For Entering
REBOOT Mode
P2.7
Hi-Z
P2.6
RST
20 US
10 mS
Hi-Z
Notes:
1. The possible situation that you need to enter REBOOT mode is when the APFlash program can not run normally and
W79E(L)548 can not jump to LDFlash to execute on chip programming function. Then you can use this REBOOT mode to
force the CPU jump to LDFlash and run on chip programming procedure. When you design your system, you can connect
the pins P26, P27 to switches or jumpers. For example in a CD ROM system, you can connect the P26 and P27 to PLAY and
EJECT buttons on the panel. When the APFlash program is fail to execute the normal application program. User can press
both two buttons at the same time and then switch on the power of the personal computer to force the W79E(L)548 to enter
the REBOOT mode. After power on of personal computer, you can release both PLAY and EJECT button. And re-run the on
chip programming procedure to let the APFlash have the normal program code. Then you can back to normal condition of
CD ROM.
2: In application system design, user must take care the P4.3, P2, P3, ALE, /EA and /PSEN pin value at reset to avoid
W79E(L)548 entering the programming mode or REBOOT mode in normal operation.
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