PIC16F688-E/P Microchip Technology, PIC16F688-E/P Datasheet - Page 400

• Manufacturer Part Number: PIC16F688-E/P
• Description: IC MCU PIC FLASH 4KX14 14DIP
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F688-E/P

• Program Memory Type: FLASH
• Program Memory Size: 7KB (4K x 14)
• Package / Case: 14-DIP (0.300", 7.62mm)
• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: UART/USART
• Peripherals: Brown-out Detect/Reset, POR, WDT
• Number Of I /o: 12
• Eeprom Size: 256 x 8
• Ram Size: 256 x 8
• Voltage - Supply (vcc/vdd): 2 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 125°C
• Processor Series: PIC16F
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 256 B
• Interface Type: SCI/USART
• Maximum Clock Frequency: 20 MHz
• Number Of Programmable I/os: 12
• Number Of Timers: 2
• Operating Supply Voltage: 2 V to 5.5 V
• Maximum Operating Temperature: + 125 C
• Mounting Style: Through Hole
• 3rd Party Development Tools: 52715-96, 52716-328, 52717-734
• Development Tools By Supplier: PG164130, DV164035, DV244005, DV164005, PG164120, ICE2000, DM163014, DM164120-4
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 8-ch x 10-bit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: AC162066 - HEADER INTRFC MPLAB ICD2 20PINAC162061 - HEADER INTRFC MPLAB ICD2 20PINDM163029 - BOARD PICDEM FOR MECHATRONICSAC162056 - HEADER INTERFACE ICD2 16F688ACICE0207 - MPLABICE 14P 300 MIL ADAPTER
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

PICmicro MID-RANGE MCU FAMILY
21.15
DS31021A-page 21-16
Design Tips
Question 1:
Answer 1:
1.
2.
3.
Question 2:
Answer 2:
After the holding capacitor is disconnected from the input channel, one T
set, the input channel may be changed.
Question 3:
Answer 3:
A very good reference for understanding A/D conversions is the “Analog-Digital Conversion
Handbook” third edition, published by Prentice Hall (ISBN 0-13-03-2848-0).
Make sure you are meeting all of the timing specifications. If you are turning the A/D mod-
ule off and on, there is a minimum delay you must wait before taking a sample, if you are
changing input channels, there is a minimum delay you must wait for this as well, and
finally there is Tad, which is the time selected for each bit conversion. This is selected in
ADCON0 and should be between 2 and 6 s. If T
converted before the conversion is terminated, and if T
the sampling capacitor can droop before the conversion is complete. These timing speci-
fications are provided in the data book in a table or by way of a formula, and should be
looked up for your specific part and circumstances.
Often the source impedance of the analog signal is high (greater than 1k ohms) so the
current drawn from the source to charge the sample capacitor can affect accuracy. If the
input signal does not change too quickly, try putting a 0.1 F capacitor on the analog input.
This capacitor will charge to the analog voltage being sampled, and supply the instanta-
neous current needed to charge the 51.2 pf internal holding capacitor.
Finally, straight from the data book: “In systems where the device frequency is low, use of
the A/D clock derived from the device oscillator is preferred...this reduces, to a large
extent, the effects of digital switching noise.” and “In systems where the device will enter
SLEEP mode after start of A/D conversion, the RC clock source selection is required. This
method gives the highest accuracy.”
I am using one of your PIC16C7X devices, and I find that the Analog to Dig-
ital Converter result is not always accurate. What can I do to improve accu-
racy?
After starting an A/D conversion may I change the input channel (for my
next conversion)?
Do you know of a good reference on A/D’s?
AD
is too short, the result may not be fully
AD
is made too long the voltage on
1997 Microchip Technology Inc.
AD
after the GO bit is