PIC16C782 Microchip Technology Inc., PIC16C782 Datasheet - Page 78

• Manufacturer Part Number: PIC16C782
• Description: 8-bit Cmos Microcontrollers With A/d, D/a, Opamp, Comparators And Psmc
• Manufacturer: Microchip Technology Inc.

PIC16C781/782
9.6.1
In systems where the device frequency is low, use of
the ADC RC clock is preferred. At moderate to high fre-
quencies, T
lator. T
when derived from T
phase clock transitions. This reduces, to a large extent,
the effects of digital switching noise. This is not possi-
ble with the RC derived clock. The loss of accuracy due
to digital switching noise can be significant if many I/O
pins are active.
In systems where the device enters SLEEP mode after
the start of the ADC conversion, the RC clock source
selection is required. In this mode, the digital noise
from the modules in SLEEP is stopped. This method
gives high accuracy.
9.7
A device RESET forces all registers to their RESET
state. This forces the ADC module to be turned off, and
any conversion is aborted.
The value that is in the ADRES register is not modified
for a Power-on Reset. The ADRES register contains
unknown data after a Power-on Reset.
9.8
If the input voltage exceeds the rail values (V
by greater than 0.2V, then the accuracy of the conver-
sion is out of specification.
An external RC filter is sometimes added for anti-
aliasing of the input signal. The R component should be
selected to ensure that the total source impedance is
kept under the 10 k recommended specification. Any
external components connected (via hi-impedance) to
an analog input pin (capacitor, zener diode, etc.) should
have very little leakage current at the pin.
DS41171A-page 76
8 s for preferred operation. This is because T
Note:
AD
Effects of a RESET
Connection Considerations
must not violate the minimum and should be
Care must be taken when using the RB2/
AN6 pin in ADC conversions due to its
proximity to the OSC1 pin.
AD
CLOCK NOISE
should be derived from the device oscil-
OSC
, is kept away from on-chip
SS
or V
Preliminary
DD
AD
)
,
9.9
The ideal transfer function of the ADC converter is as
follows: the first transition occurs when the analog input
voltage (V
9.10
A good reference for ADC converters is the "Analog-
Digital Conversion Handbook" third edition, published
by Prentice Hall (ISBN 0-13-03-2848-0).
FIGURE 9-3:
FEh
FFh
04h
03h
02h
01h
00h
Transfer Function
References
AIN
) is Analog ADC
Analog Input Voltage
ADC TRANSFER
FUNCTION
2001 Microchip Technology Inc.
REF
/256 (Figure 9-3).