NXP Semiconductors MC9S08LG16, Reference Manual

Page: 200 / 373

MC9S08LG32 MCU Series, Rev. 5
Freescale Semiconductor 200
Chapter 10
Analog-to-Digital Converter (S08ADC12V1)
10.1 Introduction
The 12-bit analog-to-digital converter (ADC) is a successive approximation ADC designed for operation
within an integrated microcontroller system-on-chip.
Figure 10-1 shows the MC9S08LG32 series with the ADC module highlighted.
10.1.1 ADC shared with LCD
PTA2/SDA/ADC0/LCD23, PTA3/KBI4/TX2/ADC1/LCD24, PTA4/KBI5/RX2/ADC2/LCD25,
PTA5/KBI6/TPM2CH0/ADC3/LCD26, PTA6/KBI7/TPM2CH1/ADC4/LCD27 and
PTA7/TPMCLK/ADC5/LCD28 share ADC functionality with LCD pins. To avoid the possibility of
placing a voltage greater than V
DD
on an ADC input, LCD functionality must be disabled for these pins
to operate as ADC pins.
As ADC inputs, these pins operate just like other ADC pins. If the ADC channel input channel voltage is
more that the LCD reference voltage (V
MCU
or V
LL3
) then there would be some leakage through the ADC
input.
10.1.2 ADC Reference and Supply Voltage
For MC9S08LG32 series devices, the ADC reference inputs (V
REFH
and V
REFL
) are shorted with the ADC
supply (V
DDA
and V
SSA
). The ADC supply must be within
±100
mV of main supply V
DD
, otherwise there
would be some leakage through the V
DDA
pad.
10.1.3 ADC Clock Gating
The bus clock to the ADC can be gated on and off using the ADC bit in SCGC1. This bit is cleared after
any reset, which disables the bus clock to this module. To conserve power, the ADC bit can be cleared to
disable the clock to this module when not in use. See
Section 5.7, “Peripheral Clock Gating ,” for more
details.