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MC80F0104/0204
Preliminary
96
Mar. 2005 Ver 0.2
20. RESET
The MC80F0104/0204 supports various kinds of reset as
below.
• Power-On Reset (POR)
• RESET (external reset circuitry)
• Watchdog Timer Timeout Reset
• Power-Fail Detection (PFD) Reset
• Address Fail Reset
Figure 20-1 RESET Block Diagram
The on-chip POR circuit holds down the device in RESET
until V
DD
has reached a high enough level for proper op-
eration. It will eliminate external components such as reset
IC or external resistor and capacitor for external reset cir-
cuit. In addition that the RESET pin can be used to normal
input port R35 by setting “POR” and “R35EN” bit Config-
uration Area(20FFH) in the Flash programming. When the
device starts normal operation, its operating parmeters
(voltage, frequency, temperature...etc) must be met.
.Table 20-1 shows on-chip hardware initialization by reset
action.
Table 20-1 Initializing Internal Status by Reset Action
The reset input is the RESET pin, which is the input to a
Schmitt Trigger. A reset in accomplished by holding the
RESET pin low for at least 8 oscillator periods, within the
operating voltage range and oscillation stable, it is applied,
and the internal state is initialized. After reset, 65.5ms (at
4 MHz) add with 7 oscillator periods are required to start
execution as shown in Figure 20-2 .
Internal RAM is not affected by reset. When V
DD
is turned
on, the RAM content is indeterminate. Therefore, this
RAM should be initialized before read or tested it.
When the RESET pin input goes to high, the reset opera-
tion is released and the program execution starts at the vec-
tor address stored at addresses FFFE
H
- FFFF
H
.
A connection for simple power-on-reset is shown in Figure
20-1 .
POR
(Power-On Reset)
Address Fail reset
PFD
(Power-Fail Detection)
WDT
(WDT Timeout Reset)
S
R
Q
BIT
Internal
RESET
RESET
Clear
Overflow
Noise Canceller
On-chip Hardware
Initial Value
On-chip Hardware
Initial Value
Program counter
(PC)
(FFFF
H
) - (FFFE
H
)
Peripheral clock
Off
RAM page register
(RPR)
0
Watchdog timer
Disable
G-flag
(G)
0
Control registers
Refer to Table 8-1 on page 25
Operation mode
Main-frequency clock
Power fail detector
Disable
Содержание MC80F0104
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