MC68HC705JP7 Datasheet, PDF (136/242 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Analog Subsystem
8.7.2.2 External Ratiometric Reference
If readings are to be ratiometric to some external source, the reference
measurement point can be connected to any one of the channel selected
pins from PB1–PB4. In this case, the reference reading can be taken by
setting the MUX bit in the AMUX which connects channel selection bus
to the pin connected to the external reference source. If the external
reference is greater than V_DD –1.5 volts, then the DHOLD bit should be
used to select the 1/2 divided input.
8.8 Voltage Comparator Features
The two internal comparators can be used as simple voltage
comparators if set up as described in Table 8-8. Both comparators can
be active in the wait mode and can directly restart the part by means of
the analog interrupt. Both comparators can also be active in the stop
mode, but cannot directly restart the part. However, the comparators can
directly drive PB4 which can then be connected externally to activate
either a port interrupt on the PA0:3 pins or the IRQ/V_PP pin.
Table 8-8. Voltage Comparator Setup Conditions
Comparator
Current
Source
Enable
Discharge
Device
Disable
Port B Pin
as Inputs
Port B Pin
Pulldowns
Disabled
1
Not
Not DDRB2 = 0 PDIB2 = 1
affected affected DDRB3 = 0 PDIB3 = 1
2
ISEN = 0
ISEN = 0
DDRB0 = 0 PDIB0 = 1
DDRB1 = 0 PDIB1 = 1
Prog. Timer
Input
Capture
Source
Not
affected
ICEN = 0
IEDG = 1
8.8.1 Voltage Comparator 1
Voltage comparator 1 is always connected to two of the port B I/O pins.
These pins should be configured as inputs and have their software
programmable pulldowns disabled. Also, the negative input of voltage
comparator 1 is connected to the PB3/AN3/TCAP and shared with the
input capture function of the 16-bit programmable timer. Therefore, the
timer input capture interrupt should be disabled so that changes in the
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MC68HC705JJ7 • MC68HC705JP7 — REV 4
Analog Subsystem
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