PIC16C923-04I/CL Microchip Technology, PIC16C923-04I/CL Datasheet - Page 87

• Manufacturer Part Number: PIC16C923-04I/CL
• Description: 8-Bit CMOS Microcontroller with LCD Driver
• Manufacturer: Microchip Technology

12.8
An A/D conversion can be started by the “special event
trigger” of the CCP1 module. This requires that the
CCP1M3:CCP1M0 bits (CCP1CON<3:0>) be pro-
grammed as 1011 and that the A/D module is enabled
(ADON bit is set). When the trigger occurs, the
GO/DONE bit will be set, starting the A/D conversion,
and the Timer1 counter will be reset to zero. Timer1 is
reset to automatically repeat the A/D acquisition period
with minimal software overhead (moving the ADRES to
the desired location). The appropriate analog input
channel must be selected and the minimum acquisition
done before the “special event trigger” sets the
GO/DONE bit (starts a conversion).
If the A/D module is not enabled (ADON is cleared),
then the “special event trigger” will be ignored by the
A/D module, but will still reset the Timer1 counter.
12.9
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-alias-
ing of the input signal. The R component should be
selected to ensure that the total source impedance is
kept under the 10 k
external components connected (via hi-impedance) to
an analog input pin (capacitor, zener diode, etc.) should
have very little leakage current at the pin.
1997 Microchip Technology Inc.
Use of the CCP Trigger
Connection Considerations
recommended specification. Any
SS
or V
DD
)
12.10
The ideal transfer function of the A/D converter is as fol-
lows: the first transition occurs when the analog input
voltage (V
FIGURE 12-5: A/D TRANSFER FUNCTION
FEh
FFh
04h
03h
02h
01h
00h
Transfer Function
AIN
) is Analog V
Analog input voltage
PIC16C9XX
REF
/ 256 (Figure 12-5).
DS30444E - page 87