PIC16F688-E/ML Microchip Technology, PIC16F688-E/ML Datasheet - Page 420

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

Specifications of PIC16F688-E/ML

• Core Size: 8-Bit
• Program Memory Size: 7KB (4K x 14)
• Core Processor: PIC
• Speed: 20MHz
• Connectivity: UART/USART
• Peripherals: Brown-out Detect/Reset, POR, WDT
• Number Of I /o: 12
• Program Memory Type: FLASH
• 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
• Package / Case: 16-QFN
• Controller Family/series: PIC16F
• No. Of I/o's: 12
• Eeprom Memory Size: 256Byte
• Ram Memory Size: 256Byte
• Cpu Speed: 20MHz
• No. Of Timers: 2
• Processor Series: PIC16F
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 256 B
• Interface Type: EUSART, RS- 232, SCI, USB
• Maximum Clock Frequency: 20 MHz
• Number Of Programmable I/os: 12
• Number Of Timers: 2
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• 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: 10 bit, 8 Channel
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: AC164324 - MODULE SKT FOR MPLAB 8DFN/16QFNXLT16QFN1 - SOCKET TRANSITION 14DIP TO 16QFNAC162061 - HEADER INTRFC MPLAB ICD2 20PINAC162056 - HEADER INTERFACE ICD2 16F688
• Lead Free Status / Rohs Status: Details

PICmicro MID-RANGE MCU FAMILY
22.13
DS31022A-page 22-18
Design Tips
Question 1:
Answer 1:
1.
2.
3.
4.
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 ADC off
and on, there is a minimum delay you must wait before taking a sample, if you are chang-
ing input channels, there is a minimum delay you must wait for this as well, and finally
there is T
ADCON0 and should be between 2 and 6 s. If T
converted before the conversion is terminated, and if Tad is made too long the voltage on
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.
On the PIC16C71, one of the analog input pins is next to an oscillator pin. Naturally if
these traces are next to each other some noise can couple from the oscillator to the ana-
log circuit. This is especially true when the clock source is an external canned oscillator,
since its output is a square wave with a high frequency component to its sharp edge, as
opposed to a crystal circuit which provides a slower rise sine wave. Again, decoupling the
analog pin can help, or if you can spare it, turn the pin into an output and drive it low. This
will really help eliminate cross coupling into the analog circuit.
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.”
AD
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?
, which is the time selected for each bit conversion. This is selected in
AD
is too short, the result may not be fully
1997 Microchip Technology Inc.
AD
after the GO bit is