Motorola GM328 Service Manual page 101

Controller Circuits 1-9
There are 8 analogue to digital converter ports (A/D) on U0101. They are labelled within the device
block as PE0-PE7. These lines sense the voltage level ranging from 0 to 5V of the input line and
convert that level to a number ranging from 0 to 255 which can be read by the software to take
appropriate action.
For example U0101-67 is the battery voltage detect line. R0671 and R0672 form a resistor divider
on INT SWB+. With 30K and 10K and a voltage range of 11V to 17V, that A/D port would see 2.74V
to 4.24V which would then be converted to ~140 to 217 respectively.
U0101-69 is the high reference voltage for the A/D ports on the µP. Capacitor C0101 filters the +5V
reference. If this voltage is lower than +5V the A/D readings will be incorrect. Likewise U0101-68 is
the low reference for the A/D ports. This line is normally tied to ground. If this line is not connected to
ground, the A/D readings will be incorrect.