NEC 78014Y Series, User Manual

Page: 254 / 547

www.DataSheet4U.com
CHAPTER 14 A/D CONVERTER
254
14.4 A/D Converter Operations
14.4.1 Basic operations of A/D converter
(1) Set the number of analog input channels with A/D converter input select register (ADIS).
(2) From among the analog input channels set with ADIS, select one channel for A/D conversion with A/D converter
mode register (ADM).
(3) Sample the voltage input to the selected analog input channel with the sample & hold circuit.
(4) Sampling for the specified period of time sets the sample & hold circuit to the hold state so that the circuit
holds the input analog voltage until termination of A/D conversion.
(5) Bit 7 of successive approximation register (SAR) is set and the tap selector sets the series resistor string
voltage tap to (1/2) AV
REF
.
(6) The voltage difference between the series resistor string voltage tap and analog input is compared with a
voltage comparator. If the analog input is larger than (1/2) AV
REF
, the MSB of SAR remains set. If the input
is smaller than (1/2) AV
REF
, the MSB is reset.
(7) Next, bit 6 of SAR is automatically set and the operation proceeds to the next comparison. In this case, the
series resistor string voltage tap is selected according to the preset value of bit 7 as described below.
• Bit 7 = 1: (3/4) AV
REF
• Bit 7 = 0: (1/4) AV
REF
The voltage tap and analog input voltage are compared and bit 6 of SAR is manipulated with the result as
follows.
• Analog input voltage
≥
Voltage tap: Bit 6 = 1
• Analog input voltage
≤
Voltage tap: Bit 6 = 0
(8) Comparison of this sort continues up to bit 0 of SAR.
(9) Upon completion of the comparison of 8 bits, any resulting effective digital value remains in SAR and the
resulting value is transferred to and latched in the A/D conversion result register (ADCR).
At the same time, the A/D conversion termination interrupt request (INTAD) can also be generated.