MC68HC11KW1 Datasheet, PDF (197/238 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor HCMOS) microcontroller unit

10
ANALOG-TO-DIGITAL CONVERTER
The analog-to-digital converter system consists of a single 10-bit successive approximation type
converter and a 16-channel multiplexer. Ten of the channels are connected to pins on the
MC68HC11KW1 (ports E and G), two are unused and the remaining four channels are dedicated
to internal reference points or test functions. The A/D converter shares input pins with port E and
port G as follows:
Pin Alternative function
PG6
AN0
PG7
AN1
PE0
AN2
PE1
AN3
PE2
AN4
PE3
AN5
PE4
AN6
PE5
AN7
PE6
AN8
PE7
AN9
There are eight 10-bit result registers, and control logic allows for four or eight consecutive
conversions before stopping, or for conversions to continue with the newest conversion overwriting
the oldest result register. Also, conversions can be performed several times on a single selected
channel, or consecutively on a selected group of four channels. In addition, the control logic can
convert eight channels and then stop, or convert continuously.
Two dedicated lines (VRH and VRL) are provided for the reference voltage inputs. These pins may
be connected to a separate or isolated power supply to ensure full accuracy of the A/D conversion.
Furthermore, the A/D converter supply pins VDDAD and VSSAD allow the user to isolate the A/D
voltage supply from the main VDD/VSS supply lines. This reduces the effects that noise from the
CPU core has on the A/D converter, thus improving accuracy.
The 10-bit A/D converter accepts analog inputs ranging from V_RL to V_RH. Smaller input ranges can
also be obtained by adjusting V_RL and V_RH to the desired upper and lower limits. Conversion is
specified and tested for V_RL = 0 volts and V_RH = 5 volts. The A/D system can be operated with V_RL
below V_DD and/or V_RL above V_SS as long as V_RH is above V_RL by enough to support the
conversions (2.5 to 5.0 volts).
10
MC68HC11KW1
ANALOG-TO-DIGITAL CONVERTER
10-1