August 27, 1998
GENERAL RELEASE SPECIFICATION
SECTION 15
ANALOG SUBSYSTEM
The analog subsystem of the MC68HC05SB7 is based on an on-chip voltage
comparator as shown in Figure 15-1.
This configuration provides following features:
•
The voltage comparator with external access to both inverting and non-
inverting inputs
•
The voltage comparator can be connected as a single-slope A/D. The
possible single-slope A/D connection provides the following features:
– A/D conversions can use V
or an external voltage as a reference
DD
with software used to calculate ratiometric or absolute results
– Channel access to up to eight inputs via multiplexer control with
independent multiplexer control allowing multiple input connections
– Access to V and V for calibration
DD
SS
– Divide by 2 to extend input voltage range
– The comparator can be inverted to calculate input offsets
– Internal sample and hold capacitor
Voltages are resolved by measuring the time it takes an external capacitor to
charge up to the level of the unknown input voltage that is being measured. The
beginning of the A/D conversion time can be started by several means:
•
•
•
Output compare from the 16-bit programmable Timer
Timer overflow from the 16-bit programmable Timer
Direct software control via a register bit
The end of the A/D conversion time can be captured by several means:
•
•
•
Input capture in the 16-bit programmable Timer
Interrupt generated by the comparator output
Software polling of the comparator output using software loop time
MC68HC05SB7
REV 2.1
ANALOG SUBSYSTEM
MOTOROLA
15-1
FREESCALE [ Freescale ]
