
S1C62740 TECHNICAL HARDWARE
EPSON
I-115
CHAPTER 5: SUMMARY OF NOTES
5.2 Summary of Notes by Function
Here, the cautionary notes are summed up by function category.
Keep these notes well in mind when programming.
Memory Memory is not mounted in unused area within the memory map
and in memory area not indicated in this manual. For this reason,
normal operation cannot be assured for programs that have been
prepared with access to these area.
Watchdog timer The watchdog timer must be reset within 3-second cycles. Because
of this, the watchdog timer data (WD0, WD1) cannot be used for
clocking of 3 seconds or more.
Oscillation circuit (1) It takes at least 5 msec from the time the OSC3 oscillation
circuit goes ON until the oscillation stabilizes. Consequently,
when switching the CPU operation clock from OSC1 to OSC3,
do this after a minimum of 5 msec have elapsed since the OSC3
oscillation went ON.
Further, the oscillation stabilization time varies depending on
the external oscillator characteristics and conditions of use, so
allow ample margin when setting the wait time.
(2) When switching the clock form OSC3 to OSC1, use a separate
instruction for switching the OSC3 oscillation OFF. An error in
the CPU operation can result if this processing is performed at
the same time by the one instruction.
(3) When shifting to the SLEEP status, the CPU clock must be set
to OSC1 and the OSC3 oscillation circuit must be OFF.
Input ports When input ports are changed from low to high by pull up resistor,
the rise of the waveform is delayed on account of the time constant
of the pull up resistor and input gate capacitance. Hence, when
fetching input ports, set an appropriate wait time.
Particular care needs to be taken of the key scan during key matrix
configuration.
Make this waiting time the amount of time or more calculated by
the following expression.
10
× C × R
C: terminal capacitance 5 pF + parasitic capacitance ? pF
R: pull up resistance 300 k
Output ports When BZ, BZ, FOUT and PTOVF are selected, a hazard may be
observed in the output waveform when the data of the output
register changes.