Samsung Microcassette Recorder 8-Bit CMOS Microcontroller Benutzerhandbuch

The A/D conversion process requires 4 steps (4 clock edges) to convert each bit and 10 clocks to set-up A/D
conversion. Therefore,  total of 50 clocks are required to complete an 10-bit conversion: When fxx/8 is selected
for conversion clock with an 4.5 MHz fxx clock frequency, one clock cycle is 1.78 us. Each bit conversion
requires 4 clocks, the conversion rate is calculated as follows:

4 clocks/bit  

×

  10-bit + set-up time = 50 clocks, 50 clock 

×

 1.78 us = 89 us at 0.56 MHz (4.5 MHz/8)

Note that A/D converter needs at least 25

µ

s for conversion time.

The A/D converter control register, ADCON, is located at address D0H in page 0. It has three functions:

— Analog input pin selection (bits 4 and 5)

— End-of-conversion status detection (bit 3)

— ADC clock selection (bits 2 and 1)

— A/D operation start or enable (bit 0 )

After a reset, the start bit is turned off. You can select only one analog input channel at a time. Other analog
input pins (AD0–AD3) can be selected dynamically by manipulating the ADCON.4–5 bits. And the pins not used
for analog input can be used for normal I/O function.

Start or enable bit
0 = Disable operation
1 = Start operation
      (Automatically disable
      the operation after
      conversion completes.)

A/D Converter Control Register (ADCON)

D0H, Page0, R/W (EOC bit is read-only)

.7

.6

.5

.4

.3

.2

.1

.0

MSB

LSB

End-of-conversion bit
0 = Not complete Conversion
1 = complete Conversion

Always logic zero

A/D input pin selection bits:
00 = AD0
01 = AD1
10 = AD2
11 = AD3

Clock Selection bits:
00 = fxx/16
01 = fxx/8
10 = fxx/4
11 = fxx/1