
S1C88409 TECHNICAL MANUAL
EPSON
201
CHAPTER 6: SUMMARY OF NOTES
A/D converter
(1) The A/D converter can operate by inputting
the clock from the prescaler. Therefore, it is
necessary to set the division ratio of the
prescaler and to turn the clock output on before
starting A/D conversion. Furthermore, it is
also necessary that the OSC3 oscillation circuit
is operating because the prescaler can operate
only when the OSC3 is set as the CPU clock.
(Refer to Section 5.5, "Prescaler and Clock
Control Circuit for Peripheral Circuits".)
(2) When SLEEP mode is set during A/D conver-
sion, correct A/D conversion result cannot be
obtained because the OSC3 oscillation circuit
stops. Do not set in SLEEP mode during A/D
conversion.
(3) The input clock and analog input terminals
should be set when the A/D converter stops.
Changing in the A/D converter operation may
cause a malfunction.
(4) The frequency of the input clock should be
lower than the maximum value shown in
Section 8.7, "A/D Converter Characteristics".
(5) To prevent malfunction, do not start A/D
conversion (writing to the CHS register) when
the A/D conversion clock is not being output
from the prescaler, and do not turn the
prescaler output clock off during A/D conver-
sion.
(6) If the CHS register selects an input channel
which is not included in the analog input
terminals set by the PAD register (the PAD
register can select several terminals simulta-
neously), the A/D conversion does not result
in a correct converted value.
(7) During A/D conversion, do not operate the
P3n terminals which are not used for analog
inputs of the A/D converter (for input/output
of digital signal and for D/A conversion). It
affects the A/D conversion precision.
D/A converter
The D/A converter should be operated only when
it is necessary in order to reduce current consump-
tion. Stop D/A conversion by writing "0" to the
DAE register if unnecessary.
Interrupt
(1) When the RETE instruction is executed without
resetting the interrupt factor flag after an
interrupt has been generated, the same inter-
rupt is generated again. Therefore, the inter-
rupt factor flag must be reset (writing "1") in
the interrupt handler routine.
(2) Be aware if the interrupt flags (I0, I1) are
rewritten (set to lower priority) prior to
resetting the interrupt factor flag after an
interrupt is generated, the same interrupt will
be generated again.
(3) An exception processing vector is fixed at 2
bytes, so it cannot specify a branch destination
bank address. Therefore, to branch from two or
more banks to a common exception handler
routine, the top portion of the exception
handler routine must be described within the
common area (000000H–007FFFH).