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2005 Microchip Technology Incorporated. All Rights Reserved. Slide 1

915 TAT

Tips & Tricks on Designingwith Microchips

6/8/14-pin Devices

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2005 Microchip Technology Incorporated. All Rights Reserved. Class Slide 2

What this class is...

TricksTricks

IdeasIdeas

TipsTips

HintsHints

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Agenda

Presentation: 1 hr

Hardware Tips and Tricks Software Tips and Tricks

Break: 10 min

Hands-on session: 3 hours

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8- and 14-pin Flash Devices

High Performance MCU DC to 20 MHz operating speed

8-level deep stack

FLASH Program Memory

Re-programmable In-Circuit Serial Programming (ICSP) capability

Low Power Consumption Low Voltage operation with EEPROM write capability

over whole voltage range (2V-5.5V)

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Tips and Trickswith Hardware

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Dual Speed RC Oscillator

PIC12F6XX

GP0OSC1

+5V

R1 R2

C

1. After reset I/O pin is High1. After reset I/O pin is High ImpedenceImpedence

(running at low frequency)(running at low frequency)

2. Output a high on I/O pin2. Output a high on I/O pin

3. R1, R2 and C determine Osc Frequency3. R1, R2 and C determine Osc Frequency

4. Works also with additional capacitors4. Works also with additional capacitors

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Screen Captures using Hewlett-Packard Mixed Signal Oscilloscope 54645

Dual Speed RC Oscillator

Freq = 2.1 MHz

Duty Cycle = 91%

Freq = 4.3 MHz

Duty Cycle = 90%

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Input/Output: Multiplexing

1 2

3 4

3V

GP0

GP1

GP2

PIC12F6XX

5 6

GPIO LEDs0 1 2 1 2 3 4 5 6

0 0 0 0 0 0 0 0 00 1 Z 1 0 0 0 0 01 0 Z 0 1 0 0 0 0Z 0 1 0 0 1 0 0 0

Z 1 0 0 0 0 1 0 00 Z 1 0 0 0 0 1 01 Z 0 0 0 0 0 0 10 0 1 0 0 1 0 1 00 1 0 1 0 0 1 0 0

0 1 1 1 0 0 0 1 01 0 0 0 1 0 0 0 1

1 0 1 0 1 1 0 0 01 1 0 0 0 0 1 0 11 1 1 0 0 0 0 0 0

Example - Six LEDs on 3 I/O pins

# LEDs = # I/Os * (# I/Os - 1) (1)

Note 1: #LEDs also limited by pin IOL, IOH and max device current.

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PICMCUI/O

Read 3 States from 1 Pin

To check state Z Drive output pin high

Set to input

Read 1

Drive output pin low

Set to input

Read 0

To check state 0 Read 0 on pin

To check state 1 Read 1 on pin

State Pin 0 Pin 1

0 closed open1 open closedZ open open

5v

0v

Pin 1

Pin 0

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4x4 Keyboard with 1 Input

GP0/AN0

PIC12F6XX

VDDResistors chosen for unique voltages

Use A/D to measure button voltage

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Decode Keys and ID SettingsDecode Keys and ID Settings

When GP4=1and no keyspressed, readID setting

When GP4=0,read switch

buttons

GP0

GP4

GP1

GP2

GP3

VDD

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Reading four switches with

one Comparator and two pins Set CVref to check for each valid level

Toggle input select to check second pair

Switches pull up to optimize range of CVref

CVref

PIC16F630

COUT

VDD

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1 Pin Power/Data

Single direction data Transistor pulls data line low via Sender GPIO Capacitor stabilizes VDD while data line low

GP0 GP0

SenderReceiver

VDD

VDD

VDD - 0.7V

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Generating High VoltagesGenerating High Voltages

CLKOUT generates frequency for charge pumpCLKOUT generates frequency for charge pump

Low costLow cost Minimal part countMinimal part count

PIC12F6XXw/ RCCLKOUT

CLKOUTVout max = (2 * VDD) - (2 * Vdiode)

CpumpCfilter

VDD

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Smart Current Limiter

Using A/D Motor control and power supplies often need

current limiter

Intelligent control can be done for: In-rush current

Current limiting

Over-current recovery

Smart circuit breaker

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Using PICmicroMCU A/D

for Smart Current Limiter

Detect current throughlow side sense resistor

Optional peak filter

capacitor Varying levels of

overcurrent response

can be realized insoftware

Rsense

10KLoad or Motor

PIC12F6XX

AN0

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1. RC timing method with reference resistor

2. Creating a Delta-Sigma ADC

Reading an Analog Sensor

Without an ADC Peripheral

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1. RC Timing Method:

Simple RC step response

Vc(t) = VDD * (1 - e -t/(RC))

t = -RC ln(1 - Vth/VDD)

Vth/VDD is constant

R2 = (t2/t1) * R1

t = 0 t = t1

Vth

Vc(t)

Time

t = t2

R1R2



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Other alternatives: Voltage comparator in the PIC12F6XX

1. Set GP1 and GP2 to inputs, andGP0 to a low output to discharge C.

2. Set GP0 to an input and GP1 to ahigh output.

3. Measure tRsen (GP0 changes to 1).4. Repeat step 1.5. Set GP0 to an input and GP2 to a

high output.

6. Measure tRref (GP0 changes to 1).7. Use film polypropylene capacitor.8. Rsen = x RreftRsen

tRref

Rref

Rsen

GP2

GP1

GP0

PIC12F6XX

1. RC Timing Method



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10K

Rsen

GP2

GP1

AN0 (A/D input)

PIC12F6XX100K

1. 10K and 100K resistors areused to set the range.

2. Set port pins for desired resistorsto output 1, others to inputs.

3. Vref for A/D = VDD.4. Rsen calculation is independent

of VDD.5. Count = Rsen/(Rsen+Rref) x 2556. Dont forget to allow acquisition

time for the A/D

Used to dynamically adjust the range as needed.

Reading a Sensor w/ Higher

Resolution

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1. GP1 average voltage = CVref2. Time base as sampling rate.

3. At the end of each time base period:- If GP1 > CVref, then GP2 Output Low.- If GP1 < CVref, then GP2 Output High.

4. Accumulate the GP2 lows overmany samples.

5. Number of samples determines resolution.

PIC12F6XX

Vin

CVref

GP2

GP1

COUT

Softwarecloses loop

Delta-Sigma Converter

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Delta-Sigma Converter

Pros:

High resolution

Good noise immunity Easy to scale and offset

the signal, even far

above VDD and belowVSS

Inherently linear andmonotonic

Requires minimalexternal components(2 Rs & 1 C)

Cons:

Requires some F/W

overhead Slow conversion

More bits = longer

conversion time Absolute accuracy

requires stable powersupply

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Tips and Trickswith Software

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NOP

NOP ;2 instructions, 2 cycles

CALL Rtrn ;1 instruction, 4 cycles. . .

Rtrn RETURN

GOTO$+1 ;1 instruction, 2 cycles

Delay Techniques

Use GOTO next instruction instead of two NOPs.

Use CALL Rtrn as quad, 1 instruction NOP (where Rtrn

is the exit label from an existing subroutine).

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Optimizing Destinations

Destination bit determines W or F for result

Look at data movement and re-structureExample: A + B => A

MOVF B,WADDWF A,F

2 instructions

MOVF A,WADDWF B,WMOVWF A

3 instructions

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Optimizing Function Calls

Subroutine . . . ; Do something

RETURN

. . .CALL Subroutine ; 2 instructions, 4 cycles

RETURN

. . .

GOTO Subroutine ; 1 instruction, 2 cycles

Replace a CALL instruction that is immediately followed

by a RETURN instruction by a GOTO instruction

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Conditional Bit Set/Clear

To move single bit of data from REGA to REGB:

Precondition REGB bit

Test REGA bit and fix REGB if necessary

BTFSS REGA,2BCF REGB,5BTFSC REGA,2BSF REGB,5

4 instructions

BCF REGB,5BTFSC REGA,2BSF REGB,5

3 instructions

Note : When controlling ports, a two cycle zero pulsecan occur

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Swap File Register with W

The following macro swaps the contents of W and

REG without using a second register

SWAP MACRO REG

XORWF REG,FXORWF REG,WXORWF REG,FENDM

Needs: 0 TEMP Registers3 Instructions

3 Tcy

W = 0xaa, REG = 0x55

1010 1010

0101 01011111 1111 (REG)

1010 1010

0101 0101 (W)

1111 1111

1010 1010 (REG)

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Rotate a byte through carry without using RAM

variable for loop count:

Easily adapted to serial protocol routines.

Carry bit is cleared (except last cycle) and the

cycle repeats until the zero bit sets indicating

the end.

Bit Shifting using Carry Bit

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Bit Shifting using Carry Bit

1

C

Z = 1

2nd Rotate

1st Rotate

Final Rotate

1 0 1 0 1 0 1 0

7 0

1 0 1 0 1 0 1 0

10 0 1 0 1 0 1 0

01 0 0 0 0 0 0 0

1

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Conclusion

Use of existing features wisely

TRIS states on I/Os

CLKOUT output

Destination locations

Simple external circuits

RC circuits Resistor ladders / dividers

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References

AN512 - ImplementingOhmmeter/Temperature Sensor

AN611 - Resistance and Capacitance MeterUsing a PIC16C622

AN683 - A Comparator Based Slope ADC

AN700 Make a Delta-Sigma ConverterUsing a Microcontroller's Analog

Comparator Module Tips and Tricks Booklet

LCD PICmicro MCU Tips 'n Tricks

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Hands-on Material

HardwareHardware

MPLABMPLAB

ICD2 Programmer / EmulatorICD2 Programmer / Emulator Demonstration boardDemonstration board

SoftwareSoftware MPLAB IDEMPLAB IDE Project templateProject template

DocumentationDocumentation HandHand--out with schematicout with schematic TipsTips n Tricks bookletn Tricks booklet

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Lets Write Some Code!

1. Multiplexing LEDs1. Multiplexing LEDs

2. Multiplexing buttons2. Multiplexing buttons

3. Reading a sensor with higher accuracy3. Reading a sensor with higher accuracy

4. BONUS: Implement a Delta4. BONUS: Implement a Delta--Sigma A/D converterSigma A/D converter

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915 Tat

Documents

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