CHAPTER 11 POWER-ON-CLEAR CIRCUITS
User’s Manual U14826EJ5V0UD
128
11.4 Power-on-Clear Circuit Operation
11.4.1 Power-on-clear (POC) circuit operation
The POC circuit compares the detection voltage (V
POC
) with the power supply voltage (V
DD
) and generates an
internal reset signal if V
DD
< V
POC
.
For mask ROM versions, it is possible to select a POC switching circuit, normally operating POC circuit, or
normally halted POC circuit by using a mask option. When a POC switching circuit is selected, POC operation can be
controlled by software. Only the POC switching circuit is available for the
µ
PD78E9860A and 78E9861A (selection
cannot be made by mask option).
Observe the following procedure when switching POC operation using the POC switching circuit.
(1) Switching from POC stopped to POC operating
<1> Check that POCMK1 = 1
<2> Clear POCMK0 to 0 to put the POC circuit into the operating state
<3> Wait until the operation stabilization time has elapsed (because the output signal is unstable, generation
of the reset signal via the POC circuit is set to disabled)
<4> Clear POCMK1 to 0 to enable generation of the reset signal via the POC circuit
(2) Switching from POC operating to POC stopped
<1> Set POCMK1 to 1 to disable generation of the reset signal via the POC circuit
<2> Set POCMK0 to 1 to put the POC circuit into the operation stopped state
Generation of the reset signal via the POC circuit can be determined by reading the POCOF1 flag. When the reset
signal is generated via the POC circuit, POCOF1 is set to 1. POCOF1 is cleared by writing 0 to POCF1
Note
.
When using the POC circuit, clear POCOF1 beforehand.
Note
POCOF1 is cleared when data is written to any of bits 0 to 2 in the POCF1 register.
Figures 11-6 to 11-8 show the timing of reset signal generation via the POC circuit.
Figure 11-6. Timing of Internal Reset Signal Generation When POC Circuit Normally Operating
Power supply voltage (V
DD
)
Detection voltage (V
POC
)
1.8 V
Time
Internal reset
signal
Содержание PD789860
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