Panasonic KX-FT21BX Service Manual page 88

KX-FT21LA
The signal lines that must be normal for the system to boot up are listed here [List 1].
For signal lines other than these, even if they malfunction they do not directly affect booting up the system.
[List 1]
‡@ D0~D7
‡A A0~A16
‡B RD
If these signals are normal, once the power is turned on, each IC repeatedly outputs 5V or 3.3V (H) and 0V (L). The following
page shows NG and normal wave patterns.
NG
(Address/Data Bus)
(Address Bus)
(Read Signal)
ROMCS (ROM Select Signal)
WR (Write Signal)
RAMCS (SRAM Select Signal)
NG Wave pattern
0V never appears.
5V or 3.3V
For a short between D0 and D1
5V never appears.
NG
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0V