MC9S12G Datasheet, PDF (116/1160 Pages) Freescale Semiconductor, Inc – Ignores external trigger. Performs one conversion sequence and stops.

Device Overview MC9S12G-Family
1.17 ADC Result Reference
MCUs of the S12G-Family are able to measure the internal reference voltage V_DDF (see Table 1-31). V_DDF
is a constant voltage with a narrow distribution over temperature and external voltage supply (see
Table A-29).
A 12-bit left justified¹ ADC conversion result of V_DDF is provided at address 0x0_4022/0x0_4023 in the
NVM’s IFR for reference.The measurement conditions of the reference conversion are listed in
Section A.15, “ADC Conversion Result Reference”. By measuring the voltage V_DDF (see Table 1-31) and
comparing the result to the reference value in the IFR, it is possible to determine the ADC’s reference
voltage V_RH in the application environment:
V_RH = _{C-----o-S---n-t--o-v---er--e--r--td--e--R--d---eR---f--ee----fr--ee---r-n--e--c--n-e--c----e-} • 5V
The exact absolute value of an analog conversion can be determined as follows:
Result = ConvertedADInput • _{C-----oS----n-t--o-v--r-e--e--r-d-t--e-R---d--e-R--f--e-e---r-f--ee---nr---e-c---ne---c--}^•--e--5--_•--V---2---_n-
With:
ConvertedADInput:
ConvertedReference:
StoredReference:
n:
Result of the analog to digital conversion of the desired pin
Result of channel “Internal_0” conversion
Value in IFR locatio 0x0_4022/0x0_4023
ADC resolution (10 bit)
CAUTION
To assure high accuracy of the V_DDF reference conversion, the NVMs must
not be programmed, erased, or read while the conversion takes place. This
implies that code must be executed from RAM. The “ConvertedReference”
value must be the average of eight consecutive conversions.
CAUTION
The ADC’s reference voltage V_RH must remain at a constant level
throughout the conversion process.
1.18 ADC VRH/VRL Signal Connection
On all S12G devices except for the S12GA192 and the S12GA240 the external VRH signal is directly
connected to the ADC’s VRH signal input. The ADC’s VRL input is connected to VSSA. (see
Figure 1-21).
1. The format of the stored V_DDF reference value is still subject to change.
MC9S12G Family Reference Manual, Rev.1.01
116
Freescale Semiconductor
This document is valid for the S12G96 and the S12G128 device. All information related to other devices is preliminary.