CHAPTER 2: POWER SUPPLY AND INITIAL RESET
I-9
The oscillation detection circuit outputs the initial reset
signal at power-on until the crystal oscillation circuit starts
oscillating, or when the crystal oscillation circuit stops
oscillating for some reason.
However, use the following reset functions at power-on
because the initial reset function by the oscillation detection
circuit may not operate normally depending on the power-on
procedure.
An initial reset can be invoked externally by making the
reset pin high. This high level must be maintained for at
least 5 ms (when oscillating frequency, fosc = 32 kHz),
because the initial reset circuit contains a noise rejection
circuit. When the reset pin goes low the CPU begins to
operate.
Another way of invoking an initial reset externally is to input
a high signal simultaneously to the input ports (K00–K03)
selected with the mask option. The specified input port pins
must be kept high for at least 4 sec (when oscillating fre-
quency fosc = 32 kHz), because of the noise rejection circuit.
Table 2.2.1 shows the combinations of input ports (K00–
K03) that can be selected with the mask option.
A
Not used
B
K00*K01
C
K00*K01*K02
D
K00*K01*K02*K03
When, for instance, mask option D (K00*K01*K02*K03) is
selected, an initial reset is executed when the signals input
to the four ports K00–K03 are all high at the same time.
If you use this function, make sure that the specified ports
do not go high at the same time during normal operation.
Oscillation detection
circuit
Reset pin (RESET)
Simultaneous high
input to input ports
(K00–K03)
Table 2.2.1
Input port combinations
