Cautions - Toshiba TLCS-90 Series Data Book

TOSHIBA TMP90C840
6. CAUTIONS
Followings are some important cautions for the user of the TMP90C840:
(1) An undefined or write-only bit of the internal I/O register is always
set to "1" when read out.
(2) The write-only bit is always calculated as "1" when internal I/O
regis~er conta~n~ng
the write-only bit is accessed by using a
read-modify-write instruction (operation between memory and immediate
address, bit set/rese·t instruction, etc.).
(3) The system adopts the pipeline processing in which it pre fetches a 1
byte instruction. Thus a jump instruction may cause the system to
fetch the instruction that follows the jump instruction. This may
also occur for call or return instruction.
(4) If an undefined code is executed, no subsequent operation will be
guaranteed.
(5)
The internal watchdog timer is returnd to the "enable" mode by
resetting. If this function is not required, the watchdog timer
should be placed in the "disable" mode.
(6) After the power is turned on, no internal device can be reset until
the oscillator starts its operation, placing the output and I/O ports
in the undefined state. In order to define their status, a separate
external circuit is required.
MPU90-140