HT45F4M Datasheet, PDF (92/138 Pages) Holtek Semiconductor Inc – Lithium Battery Backup Power ASSP MCU

HT45F4M
Lithium Battery Backup Power ASSP MCU
Controlling the power on/off function of the A/D converter circuitry is implemented using the
ADOFF bit in the ADCR0 register. This bit must be zero to power on the A/D converter. When the
ADOFF bit is cleared to zero to power on the A/D converter internal circuitry a certain delay, as
indicated in the timing diagram, must be allowed before an A/D conversion is initiated. Even if no
pins are selected for use as A/D inputs by clearing the ACE7~ACE0 bits in the ACERL registers, if
the ADOFF bit is zero then some power will still be consumed. In power conscious applications it
is therefore recommended that the ADOFF is set high to reduce power consumption when the A/D
converter function is not being used.
The reference voltage supply to the A/D Converter can be supplied from either the positive power supply
pin, VDD, or from an external reference sources supplied on pin VREF. The desired selection is made
using the VREFS bit. As the VREF pin is pin-shared with other functions, when the VREFS bit is set
high, the VREF pin function will be selected and the other pin functions will be disabled automatically.
A/D Input Pins
All of the A/D analog input pins are pin-shared with the I/O pins on Port A as well as other
functions. The ACE7~ACE0 bits in the ACERL registers, determine whether the input pins are setup
as A/D converter analog inputs or whether they have other functions. If the ACE7~ACE0 bits for its
corresponding pin is set high then the pin will be setup to be an A/D converter input and the original
pin functions disabled. In this way, pins can be changed under program control to change their
function between A/D inputs and other functions. All pull-high resistors, which are setup through
register programming, will be automatically disconnected if the pins are setup as A/D inputs. Note
that it is not necessary to first setup the A/D pin as an input in the PAC port control register to enable
the A/D input as when the ACE7~ACE0 bits enable an A/D input, the status of the port control
register will be overridden.
The A/D converter has its own reference voltage pin, VREF, however the reference voltage can
also be supplied from the power supply pin, a choice which is made through the VREFS bit in the
ADCR1 register. The analog input values must not be allowed to exceed the value of VREF.
P A 0 /A N 0 P A 7 /A N 7 A N 8
1 .2 5 V
A C S 4~A C S 0
In p u t V o lta g e
B u ffe r
VBG EN
1 2 - b it A D C
V REF
VR EFS
VDD
P A 1 /V R E F
B andgap
R e fe re n c e
V o lta g e
A/D Input Structure
Rev. 1.10
92
January 15, 2013