
A/D CONVERTER  
S3C94A5/F94A5 
15-2 
CONVERSION TIMING 
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. 
A/D CONVERTER CONTROL REGISTER (ADCON)
The A/D converter control register, ADCON, is located at address D1H in page 0. It has three functions: 
— Analog input pin selection (bits 4, 5, 6 and 7)  
— 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–AD15) can be selected dynamically by manipulating the ADCON.4–.7 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)
D1H, 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
A/D input pin selection bits:
0000 = AD0
0001 = AD1
0010 = AD2
0011 = AD3
0100 = AD4
0101 = AD5
0110 = AD6
0111 = AD7
1000 = AD8
1001 = AD9
1010 = AD10
1011 = AD11
1100 = AD12
1101 = AD13
1110 = AD14
1111 = AD15
Clock Selection bits:
00 = fxx/16
01 = fxx/8
10 = fxx/4
11 = fxx/1
Figure 15-1. A/D Converter Control Register (ADCON)