BH67F2470 Datasheet, PDF (131/240 Pages) Holtek Semiconductor Inc – Glucose Meter Flash MCU with LCD

BH67F2470
Glucose Meter Flash MCU with LCD
A/D Converter Reference Voltage
The reference voltage supply to the A/D converter can be supplied from the power supply VDD, the
DAC reference voltage VDACVREF or from an external reference source supplied on pin VREF. The
desired selection is made using the SAVRS1 and SAVRS0 bits. When the SAVRS bit field is set to
"01", the A/D converter reference voltage will come from the internal power VDD. When the SAVRS
bit field is set to "10", the A/D converter reference voltage will come from the DAC reference
voltage VDACVREF. When the SAVRS bit field is set to "00" or "11", the A/D converter reference
voltage will come from the external VREF pin. However, if the internal A/D converter power or the
DAC reference voltage is selected as the reference voltage, the VREF pin must not be configured as
the reference voltage input function for the A/D converter to avoid the unpredictable situations. The
analog input values must not be allowed to exceed the value of the selected reference voltage.
A/D Converter Input Signals
All the external A/D analog channel input pins are pin-shared with the I/O pins as well as other
functions. The corresponding control bits for each A/D external input pin in the PCS0 register
determine whether the input pins are setup as A/D converter analog inputs or whether they have
other functions. If the pin is setup to be as an A/D analog channel input, the original pin functions
will be 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 port control register to enable the A/D
input as when the pin-shared function control bits enable an A/D input, the status of the port control
register will be overridden.
There are four internal analog signals derived from the OPA output voltage or DAC output
signal, which can be connected to the A/D converter as the analog input signal by configuring
the SAINS2~SAINS0 bits. If the external channel input is selected to be converted, the
SAINS2~SAINS0 bits should be set to "000" or "101~111" and the SACS3~SACS0 bits can
determine which external channel is selected. If the internal analog signal is selected to be
converted, the SACS3~SACS0 bits must be configured with a value from 0100 to 1111 to switch off
the external analog channel input. Otherwise, the internal analog signal will be connected together
with the external channel input. This will result in unpredictable situations.
SAINS[2:0]
000, 101~111
001
010
011
100
SACS[3:0]
0000~0011
0100~1111
0100~1111
0100~1111
0100~1111
0100~1111
Input Signals
AN0~AN3
—
OPS0
OPS1
OPS2
DACO
Description
External pin analog input
Non-existed channel, input is floating.
OPA output
OPA output
OPA output
DAC output
A/D Converter Input Signal Selection
Rev. 1.00
131
March 15, 2017