PIC16F877-04E/PT Microchip Technology, PIC16F877-04E/PT Datasheet - Page 453

• Manufacturer Part Number: PIC16F877-04E/PT
• Description: IC MCU FLASH 8KX14 EE 44TQFP
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F877-04E/PT

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 4MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 33
• Program Memory Size: 14KB (8K x 14)
• Program Memory Type: FLASH
• Eeprom Size: 256 x 8
• Ram Size: 368 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: External
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 44-TQFP, 44-VQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: PIC16F87704E/PT

Resolution
.
Slope A/D
1997 Microchip Technology Inc.
(Bits)
16
14
12
10
Conversion
Time (ms)
16.384
4.096
1.024
0.256
The selection of the external capacitor is determined by the desired characteristics of the appli-
cation. These include
• Input Voltage Range (widest range of all input channels)
• Conversion Time
• Programmable Current Source Output Values
The selection of these values should be done to minimize the time between a comparator trip
(ADCIF bit is set) to the ADTMR overflow (OVFIF is set). This ensures that the entire range of
the ADTMR is used for the A/D conversion process.
The equation for selecting the ramp capacitor value is:
Table 24-2
time, and full scale voltage measurement.
This capacitor on the CDAC pin should have a low voltage-coefficient as found in teflon, polypro-
pylene, or polystyrene capacitors, for optimum results. This external capacitor must be dis-
charged at the beginning of each conversion cycle by setting the ADRST bit (ADCON0<1>). The
time for the ADRST bit to be set depends on the characteristics of the external capacitor for a
complete discharge.
Table 24-2: External Capacitor Selection (@ 4 MHz)
Capacitor = (conversion time in seconds) X
(Volts)
Scale
Full
3.5
2.0
1.5
3.5
2.0
1.5
3.5
2.0
1.5
3.5
2.0
1.5
provides example capacitor values for the desired Slope A/D resolution, conversion
(current source output in amps) / (full scale in volts)
ADDAC3:ADDC0
Slope A/D Current Source Select
1100
1010
1011
1101
1011
1100
1101
1001
1010
1011
1010
1011
Section 24. Slope A/D
Typical Output
( amps)
24.75
29.25
24.75
29.25
20.25
24.75
24.75
22.5
22.5
22.5
27
27
Calculated
Capacitor
0.126 F
0.184 F
0.270 F
50.7 nF
73.7 nF
8.56 nF
10.4 nF
15.4 nF
1.81 nF
2.88 nF
4.22 nF
CDAC
34 nF
DS31024A-page 24-11
Nearest Standard
CDAC Capacitor
0.12 F
0.18 F
0.27 F
8.2 nF
1.8 nF
2.7 nF
3.9 nF
Value
33 nF
47 nF
68 nF
10 nF
15 nF
24