PIC18F2455-I/SP Microchip Technology Inc., PIC18F2455-I/SP Datasheet - Page 181

• Manufacturer Part Number: PIC18F2455-I/SP
• Description: Microcontroller; 24 KB Flash; 2048 RAM; 256 EEPROM; 24 I/O; 28-Pin-SPDIP
• Manufacturer: Microchip Technology Inc.

Specifications of PIC18F2455-I/SP

• A/d Inputs: 10-Channel, 10-Bit
• Comparators: 2
• Cpu Speed: 12 MIPS
• Eeprom Memory: 256 Bytes
• Input Output: 23
• Interface: I2C/SPI/USART/USB
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 28-pin SPDIP
• Programmable Memory: 24K Bytes
• Ram Size: 2K Bytes
• Speed: 48 MHz
• Timers: 1-8-bit, 3-16-bit
• Voltage, Range: 2-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

16.2
The ADCON2 register allows the user to select an
acquisition time that occurs each time the GO/DONE
bit is set. It also gives users the option to use an
automatically determined acquisition time.
Acquisition time may be set with the ACQT2:ACQT0
bits (ADCON2<5:3>) which provide a range of 2 to
20 T
continues to sample the input for the selected
acquisition
conversion. Since the acquisition time is programmed,
there may be no need to wait for an acquisition time
between selecting a channel and setting the GO/DONE
bit.
Manual
ACQT2:ACQT0 = 000. When the GO/DONE bit is set,
sampling is stopped and a conversion begins. The user
is responsible for ensuring the required acquisition time
has passed between selecting the desired input
channel and setting the GO/DONE bit. This option is
also the default Reset state of the ACQT2:ACQT0 bits
and is compatible with devices that do not offer
programmable acquisition times.
In either case, when the conversion is completed, the
GO/DONE bit is cleared, the ADIF flag is set and the
A/D begins sampling the currently selected channel
again. If an acquisition time is programmed, there is
nothing to indicate if the acquisition time has ended or
if the conversion has begun.
TABLE 16-1:
© 2006 Microchip Technology Inc.
Note 1:
AD
. When the GO/DONE bit is set, the A/D module
2:
3:
4:
Selecting and Configuring
Acquisition Time
Operation
The RC source has a typical T
The RC source has a typical T
For device frequencies above 1 MHz, the device must be in Sleep for the entire conversion or the A/D
accuracy may be out of specification.
Low-power devices only.
16 T
32 T
64 T
acquisition
2 T
4 T
8 T
time,
RC
OSC
OSC
OSC
OSC
OSC
OSC
(3)
AD Clock Source (T
T
AD
then
vs. DEVICE OPERATING FREQUENCIES
automatically
is
selected
ADCS2:ADCS0
AD
)
AD
AD
000
100
001
101
010
110
x11
begins
Advance Information
time of 1.2 s.
time of 2.5 s.
when
a
16.3
The A/D conversion time per bit is defined as T
A/D conversion requires 11 T
The source of the A/D conversion clock is software
selectable. There are seven possible options for T
• 2 T
• 4 T
• 8 T
• 16 T
• 32 T
• 64 T
• Internal RC Oscillator
For correct A/D conversions, the A/D conversion clock
(T
minimum T
more information).
Table 16-1 shows the resultant T
the device operating frequencies and the A/D clock
source selected.
AD
PIC18FXXXX
22.86 MHz
) must be as short as possible but greater than the
11.43 MHz
1.00 MHz
2.86 MHz
5.71 MHz
40.0 MHz
40.0 MHz
OSC
OSC
OSC
OSC
OSC
OSC
Selecting the A/D Conversion
Clock
PIC18F2450/4450
Maximum Device Frequency
AD
(1)
(see parameter 130 in Table 21-18 for
AD
PIC18LFXXXX
per 10-bit conversion.
AD
1.00 MHz
11.43 MHz
22.86 MHz
22.86 MHz
2.86 MHz
5.72 MHz
1.43 kHz
DS39760A-page 179
times derived from
(2)
(4)
AD
. The
AD
: