Z51F3220FNX Datasheet, PDF (181/312 Pages) Zilog, Inc. – Z8051 Series 8-Bit Microcontrollers

Z51F3220
Product Specification
11.11 12-Bit A/D Converter
11.11.1 Overview
The analog-to-digital converter (A/D) allows conversion of an analog input signal to corresponding 12-bit digital
value. The A/D module has eight analog inputs. The output of the multiplexer is the input into the converter which
generates the result through successive approximation. The A/D module has four registers which are the A/D
converter control high register (ADCCRH), A/D converter control low register (ADCCRL), A/D converter data high
register (ADCDRH), and A/D converter data low register (ADCDRL). The channels to be converted are selected
by setting ADSEL[3:0]. To execute A/D conversion, TRIG[2:0] bits should be set to ‘xxx’. The register ADCDRH
and ADCDRL contains the results of the A/D conversion. When the conversion is completed, the result is loaded
into the ADCDRH and ADCDRL, the A/D conversion status bit AFLAG is set to ‘1’, and the A/D interrupt is set.
During A/D conversion, AFLAG bit is read as ‘0’.
11.11.2 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 58 clocks are required to complete a 12-bit conversion: When fxx/8 is selected for
conversion clock with a 12MHz fxx clock frequency, one clock cycle is 0.66 μs. Each bit conversion requires 4
clocks, the conversion rate is calculated as follows:
4 clocks/bit × 12 bits + set-up time = 58 clocks,
58 clock × 0.66 μs = 38.28 μs at 1.5 MHz (12 MHz/8)
NOTE) The A/D converter needs at least 20 μs for conversion time. So you must set the conversion time more
than 20 μs.
PS029902-0212
PRELIMINARY
178