HT56RB27 Datasheet, PDF (51/153 Pages) Holtek Semiconductor Inc – TinyPowerTM A/D Type Smart Card OTP MCU with DAC, ISO 7816 and USB Interfaces

HT56RB27
TinyPower^TM A/D Type Smart Card OTP MCU
with DAC, ISO 7816 and USB Interfaces
A/D Converter Control Registers - ADCR, ADPCR, ACSR
To control the function and operation of the A/D converter, three control registers known as ADCR,
ADPCR and ACSR are provided. These 8-bit registers define functions such as the selection of which
analog channel is connected to the internal A/D converter, which pins are used as analog inputs and
which are used as normal I/Os, the A/D clock source as well as controlling the start function and
monitoring the A/D converter end of conversion status.
The ACS2~ACS0 bits in the ADCR register define the channel number. As the device contains only
one actual analog to digital converter circuit, each of the individual 8 analog inputs must be routed to
the converter. It is the function of the ACS2~ACS0 bits in the ADCR register to determine which
analog channel is actually connected to the internal A/D converter.
The ADPCR control register contains the PCR7~PCR0 bits which determine which pins on Port A are
used as analog inputs for the A/D converter and which pins are to be used as normal I/O pins. If the
PCRn bit has a value of 1, the related pin on PORT A will be set as an analog input. If the PCRn bit is
set to zero, then the related pin on Port A will be setup as a normal I/O pin.
ACSR Register
Bit
Name
R/W
POR
7
TEST
R/W
1
6
ADONB
R/W
1
5
ACS4
R/W
0
4
VBGEN
R/W
0
3
VREFS
R/W
0
2
ADCS2
R/W
0
1
ADCS1
R/W
0
0
ADCS0
R/W
0
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2~0
TEST: For test only, read as 1
ADONB: A/D Converter enable control
0: A/D converter is turned off
1: A/D converter is turned on
ACS4: Internal Band-gap reference voltage channel input selection
0: A/D converter analog channel is connected to the analog input from AN0 to AN/7
1: A/D converter analog channel is connected to the internal Band-gap voltage VBG
VBGEN: Band-gap reference voltage enable control
0: Band-gap voltage V_BG is disabled and connected to the ground
1: Band-gap voltage V_BG is enabled
The band-gap reference voltage V_BG is used for the A/D converter and LVD/LVR function, which
is controlled by the band-gap reference voltage enable bit VBGEN in the ACSR register. If the
VBG is not used for the A/D converter and the LVD/LVR function is disabled, the microcontroller
hardware will automatically turned off the band-gap reference voltage to conserve power. Care
must be taken as when the VREFS bit is set high for the A/D converter, then a V_BG turn on time
t_BG must be allowed before any A/D conversions are implemented.
VREFS: A/D converter reference voltage selection bit
0: from the internal voltage AV_DD
1: from the external pin VREF
The A/D reference voltage can come from either the internal voltage AVDD or the external
voltage V_REF, which is selected by the VREFS bit in the ACSR register. When the VREFS bit
is cleared to 0, the reference voltage of the A/D converter comes from the internal A/D power
supply VADD and the external VREF pin can be used as an I/O pin or other pin-shared function.
When the VREFS bit is set to 1, the reference voltage of the A/D converter comes from the
external VREF pin and the I/O or other pin-shared functions are disabled.
ADCS2~ADCS0: Select A/D converter clock source
000: f_SYS/2
001: f_SYS/8
010: f_SYS/32
011: undefined
100: f_SYS
101: fSYS/4
110: f_SYS/16
111: undefined
Rev. 1.20
51
April 26, 2013