PD17012_15 Datasheet, PDF (274/320 Pages) Renesas Technology Corp – 4-BIT SINGLE-CHIP MICROCONTROLLERS WITH DIGITAL TUNING SYSTEM HARDWARE

µPD17012, 17P012
22.3.2 CE reset when clock stop (STOP s) instruction is used
Figure 22-3 shows the operation of CE reset when the clock stop (STOP s) instruction is used.
When the STOP s instruction is used, the IRES, RES, and RESET signals are output as soon as the STOP
s instruction has been executed.
At this time, the basic timer clock select register of the control registers is initialized to 0000B by the RES
signal, the basic timer 0 carry FF setting signal is set to 100 ms.
Because the IRES signal is output while the CE pin is low, the halt status, which can be released by the basic
timer 0 carry, is forcibly set.
However, the device stops operation because the clock is stopped.
When the CE pin goes high, the clock stop status is released, and oscillation starts.
Because the halt status that can be released by the basic timer 0 carry is set at this time by the IRES signal,
the program starts from address 0 when the CE pin goes high and then the basic timer 0 carry FF setting pulse
rises.
Because the basic timer 0 carry FF setting pulse is initialized to 100 ms, CE reset is effected 50 ms after the
CE pin has gone high.
Figure 22-3. CE Reset Operation When Clock Stop Instruction Is Used
VDD
CE
XOUT
Basic timer 0 carry
FF setting pulse
IRES
RES
RESET
5V
0V
H
L
H
L
H
L
H
L
H
L
H
L
Normal operation
Clock stop status Halt status
50 ms
Stop s instruction Clock oscillation starts
Stop released
CE reset
Program starts from address 0.
22.3.3 Notes on CE reset
Because CE reset is effected regardless of the instruction under execution, the following points <1> and <2>
must be noted.
(1) Time to execute timer processing such as watch
When developing a watch program by using basic timer 0 or basic timer 1, the processing of that program
must be completed within a specific time.
For details, refer to 12.2.6 Notes on using basic timer 0 and 12.3.5 Notes on using basic timer 1.
(2) Processing of data and flag used for program
Care must be exercised in rewriting the contents of data or a flag that cannot be processed with one
instruction and whose contents must not change even when CE reset is effected, such as a security code.
This is explained in detail using the following examples.
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Data Sheet U10101EJ4V0DS