Rev. 1.6
69
C8051F310/1/2/3/4/5/6/7
Figure 7.3. Comparator Hysteresis Plot
The Comparator hysteresis is software-programmable via its Comparator Control register CPTnCN (for
n = 0 or 1). The user can program both the amount of hysteresis voltage (referred to the input voltage) and
the positive and negative-going symmetry of this hysteresis around the threshold voltage.
The Comparator hysteresis is programmed using Bits3-0 in the Comparator Control Register CPTnCN
(shown in SFR Definition 7.1 and SFR Definition 7.4). The amount of negative hysteresis voltage is
determined by the settings of the CPnHYN bits. As shown in Table 7.1, settings of 20, 10 or 5 mV of
negative hysteresis can be programmed, or negative hysteresis can be disabled. In a similar way, the
amount of positive hysteresis is determined by the setting the CPnHYP bits.
Comparator interrupts can be generated on both rising-edge and falling-edge output transitions. (For Inter-
rupt enable and priority control, see Section “8.3. Interrupt Handler” on page 91). The CPnFIF flag is set
to logic 1 upon a Comparator falling-edge interrupt, and the CPnRIF flag is set to logic 1 upon the Compar-
ator rising-edge interrupt. Once set, these bits remain set until cleared by software. The output state of the
Comparator can be obtained at any time by reading the CPnOUT bit. The Comparator is enabled by set-
ting the CPnEN bit to logic 1, and is disabled by clearing this bit to logic 0.
The output state of the Comparator can be obtained at any time by reading the CPnOUT bit. The Compar-
ator is enabled by setting the CPnEN bit to logic 1, and is disabled by clearing this bit to logic 0.
Note that false rising edges and falling edges can be detected when the comparator is first powered-on or
if changes are made to the hysteresis or response time control bits. Therefore, it is recommended that the
rising-edge and falling-edge flags be explicitly cleared to logic 0 a short time after the comparator is
enabled or its mode bits have been changed. This Power Up Time is specified in Table 7.1 on page 76.
Positive Hysteresis Voltage
(Programmed with CP0HYP Bits)
Negative Hysteresis Voltage
(Programmed by CP0HYN Bits)
VIN-
VIN+
INPUTS
CIRCUIT CONFIGURATION
+
_
CP0+
CP0-
CP0
VIN+
VIN-
OUT
VOH
Positive Hysteresis
Disabled
Maximum
Positive Hysteresis
Negative Hysteresis
Disabled
Maximum
Negative Hysteresis
OUTPUT
VOL
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