EM78P809NP datasheet(34/75 Pages) EMC

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EM78P809N

8-Bit Microcontroller

•

Product Specification (V1.0) 07.26.2005

(This specification is subject to change without further notice)

ADC

(Successive Approximation)

AD7 (P97)

AD6 (P96)

AD5 (P95)

AD4 (P94)

AD3 (P93)

AD2 (P92)

AD1 (P91)

AD0 (P90)

7 - 0

4 to 1

MUX

Fosc/4

Fosc/16

Fosc/32

9 8 7 6 5 4 3 2 1 0

DATA BUS

IMR1

ISFR1

ADCR

ADIC

VDD

VREF

Start to Convert

Power Down

ADCR

Fig. 6. AD Converter

It is a 10-bit successive approximation type AD converter. The upper side of analog

reference voltage can select either internal VDD or external input pin P97 (VREF) by

setting the ADREF bit in ADCR.

ADC Data Register:

When the A/D conversion is complete, the result is loaded to the ADDH (8 bit) and

ADDL (2 bit). The START/END bit is cleared, and the ADIF is set.

A/D Sampling Time:

The accuracy, linearity, and speed of the successive approximation A/D converter are

dependent on the properties of the ADC. 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 2 µs for each K

Ω

of the analog source impedance and at least 2 µs for the low-impedance source. The

maximum recommended impedance for the analog source is 10K

Ω at VDD =5V. After

the analog input channel is selected, this acquisition time must be done before A/D

conversion can be started.

A/D Conversion Time:

ADCK0 and ADCK1 select the conversion time (Tct), in terms of instruction cycles.

This allows the MCU to run at maximum frequency without sacrificing accuracy of A/D

conversion. For the EM78P809N, the conversion time per bit is about 4µs. Table 5

shows the relationship between Tct and the maximum operating frequencies.

EM78P809NP Datasheet(PDF) 34 Page - ELAN Microelectronics Corp

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