PIC16C770 Microchip Technology Inc., PIC16C770 Datasheet - Page 105

• Manufacturer Part Number: PIC16C770
• Description: 18/20-pin, 8-bit Cmos Microcontrollers With 10/12-bit A/d
• Manufacturer: Microchip Technology Inc.

10.1
The bandgap module generates a stable voltage refer-
ence of over a range of temperatures and device sup-
ply voltages. This module is enabled anytime any of the
following are enabled:
• Brown-out Reset
• Low-voltage Detect
• Either of the internal analog references (VRH,
Whenever the above are all disabled, the bandgap
module is disabled and draws no current.
10.2
The bandgap output voltage is used to generate two
stable references for the A/D converter module. These
references are enabled in software to provide the user
with the means to turn them on and off in order to min-
imize current consumption. Each reference can be indi-
vidually enabled.
The VRH reference is enabled with control bit VRHEN
(REFCON<7>). When this bit is set, the gain amplifier
is enabled. After a specified start-up time a stable ref-
erence of 4.096V nominal is generated and can be
used by the A/D converter as a reference input.
FIGURE 10-1: BLOCK DIAGRAM OF LVD AND VOLTAGE REFERENCE CIRCUIT
VRL)
2002 Microchip Technology Inc.
RA1/AN1/LVDIN
Bandgap Voltage Reference
Internal V
LVDEN
REF
V
DD
for A/D Converter
BODEN
BGAP
LVDEN
The VRL reference is enabled by setting control bit
VRLEN (REFCON<6>). When this bit is set, the gain
amplifier is enabled. After a specified start-up time a
stable reference of 2.048V nominal is generated and
can be used by the A/D converter as a reference input.
Each voltage reference is available for external use via
VRL and VRH pins.
Each reference, if enabled, can be output on an exter-
nal pin by setting the VRHOEN (high reference output
enable) or VRLOEN (low reference output enable) con-
trol bit. If the reference is not enabled, the VRHOEN
and VRLOEN bits will have no effect on the corre-
sponding pin. The device specific pin can then be used
as general purpose I/O.
Note:
PIC16C717/770/771
LVDCON
If VRH or VRL is enabled and the other ref-
erence (VRL or VRH), the BOR, and the
LVD modules are not enabled, the band-
gap will require a start-up time before the
bandgap reference is stable. Before using
the internal VRH or VRL reference, ensure
that the bandgap reference voltage is sta-
ble by monitoring the BGST bit in the LVD-
CON register. The voltage references will
not be reliable until the bandgap is stable
as shown by BGST being set.
VRHEN + VRLEN
generates
LVDIF
REFCON
VRL
VRH
DS41120B-page 103