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EM78P259N/260N
8-Bit Microprocessor with OTP ROM
Product Specification (V1.2) 05.18.2007
• 47
(This specification is subject to change without further notice)
6.7.2 ADC Data Register (ADDATA/RB, ADDATA1H/RC,
ADDATA1L/RD)
When the AD conversion is completed, the result is loaded to the ADDATA, ADDATA1H
and ADDATA1L registers. The ADRUN bit is cleared, and the ADIF is set.
6.7.3 ADC Sampling Time
The accuracy, linearity, and speed of the successive approximation of AD converter are
dependent on the properties of the ADC and the comparator. The source impedance
and the internal sampling impedance directly affect the time required to charge the
sample holding capacitor. The application program controls the length of the sample
time to meet the specified accuracy. Generally speaking, the program should wait for
2μs for each KΩ of the analog source impedance and at least 2μs for the
low-impedance source. The maximum recommended impedance for analog source is
10KΩ at Vdd=5V. After the analog input channel is selected, this acquisition time must
be done before the conversion is started.
6.7.4 AD Conversion Time
CKR1 and CKR0 select the conversion time (Tct), in terms of instruction cycles. This
allows the MCU to run at a maximum frequency without sacrificing the AD conversion
accuracy. For the EM78P259N/260N, the conversion time per bit is about 4μs. The
table below shows the relationship between Tct and the maximum operating
frequencies.
CKR1:CKR0
Operation
Mode
Max. Operation
Frequency
Max. Conversion
Rate/Bit
Max. Conversion Rate
00 Fosc/16 4 MHz 250kHz (4μs) 15*4μs=60μs (16.7kHz)
01 Fosc/4 1 MHz 250kHz (4μs) 15*4μs=60μs (16.7kHz)
10 Fosc/64 16 MHz 250kHz ( 4μs) 15*4μs=60μs (16.7kHz)
11 Internal RC – 14kHz (71μs) 15*71μs=1065μs (0.938kHz)
NOTE
■ Pin not used as an analog input pin can be used as a regular input or output pin.
■ During conversion, do not perform output instruction to maintain precision for all of
the pins.
6.7.5 ADC Operation during Sleep Mode
In order to obtain a more accurate ADC value and reduce power consumption, the AD
conversion remains operational during sleep mode. As the SLEP instruction is
executed, all the MCU operations will stop except for the Oscillators TCC, TCCA,
TCCB, TCCC and AD conversion.
The AD Conversion is considered completed as determined by:
1. ADRUN bit of R9 register is cleared (“0” value).
2. ADIF bit of RE register is set to “1”.