implementing an rc5 infrared transmitter using the ir ... · pdf fileimplementing an rc5...

June 2010 Doc ID 15550 Rev 2 1/21

AN2957Application note

Implementing an RC5 infrared transmitterusing the IR timer modulator of the STM8L10x microcontroller

IntroductionIR (infrared) light is a popular means of wireless communication for remote control applications. Many different protocol standards such as RC5, RC5x, RC6,… exist for transmitting commands via an infrared wireless interface.

This application note describes the widely-used RC5 coding scheme from Philips and presents a full working solution that implements a remote control device.

This application uses the STM8L10x microcontroller, it contains a powerful hardware modulator called IRTIM that combines signals from two internal timers to drive the IR interface. This feature makes the microcontroller especially well suited for applications that require IR signal generation capability.

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Contents AN2957

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Contents

1 STM8L10x IR interface description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 RC5 coding scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1 Frame header description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2 Device addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.3 Device instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.4 Bit descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.5 RC5 frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.6 RC5 carrier frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3 Software description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.2 RC5 functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.3 RC5 flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.4 Application flowcharts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4 Application description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

5 Hardware description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

AN2957 STM8L10x IR interface description

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1 STM8L10x IR interface description

The IR digital interface is designed to output a digital signal to an infrared diode driver circuit.

It can output a signal using any of the existing modulation styles, the modulation style is dependent on the software algorithm.

The IR interface is very easy to configure and it uses 2 signals provided by two of the STM8L10x timers (TIM2 and TIM3).

TIM2 is used to provide the Carrier Frequency and TIM3 provides the actual signal to be sent.

Figure 1. IRTIM input and output signals

TIM2_CH1(Carrier frequency)

TIM3_CH1 (Main signal)

IRTIMIRTIM_Output

RC5 coding scheme AN2957

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2 RC5 coding scheme

The RC5 coding scheme from Philips is a standard in infrared wireless command transmission.

The RC5 coding scheme can generate 2048 different commands organized on 32 groups, each group has 64 different commands.

The RC5 frame is a 14-bit word, composed of 3 parts:

● Header (3 bits)

● Device Address (5 bits)

● Device Instruction (6 bits)

The bits are transmitted in bi-phase code (also known as Manchester code) as shown in Figure 3.

The RC5 carrier frequency is 36 kHz.

Figure 2. RC5 frame format

Figure 3. Manchester coding

Header (3 bits) Device address (5 bits) Device instruction (6 bits)

Logic 0 Logic 1

AN2957 RC5 coding scheme

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2.1 Frame header descriptionThe frame header is composed of three bits: The two first bits are start bits, which always have the value "1". The next bit is a control bit, which is toggled every time a button is pressed on the remote control transmitter (to determine whether a button is pressed and held down, or pressed and released continuously).

Figure 4 and Figure 5 show examples of RC5 frame headers:

Figure 4. Frame header 1

Figure 5. Frame header 2

1 1 0

Head1 (1st press)

1 1 1

Head2 (2nd press)


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2.2 Device addressesThe device address sequence is five bits long, allowing the control of up to 32 devices (25 = 32 addresses). Table 1 gives the addresses of the controlled devices.

Table 1. RC5 device addresses

Address Device

0 TV1

1 TV2

2 Videotext

3 Extension for TV1 and TV2

4 Laser vision player

5 VCR1

6 VCR2

7 Reserved

8 SAT1

9 Extension for VCR1 and VCR2

10 SAT2

11 Reserved

12 CD-video

13 Reserved

14 CD-photo

15 Reserved

16 Audio1 preamplifier

17 Tuner

18 Analogical magneto cassette

19 Audio2 preamplifier

20 CD

21 Rack audio

22 Satellite receiver

23 DCC Magneto

24 Reserved

25 Reserved

26 CD writable

27 to 31 Reserved (for experimental use)


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2.3 Device instructionsThe instruction sequence is six bits long, allowing up to 64 (26) different instructions per address.

There are two groups of instructions, the first group is common for all devices, the second group is reserved for television devices (TV1 and TV2).

Common instructions are given in Table 2 and TV instructions are given in Table 3.

Table 2. RC5 common instructions

Common instruction Description

0 0

1 1

2 2

3 3

4 4

5 5

6 6

7 7

8 8

9 9

16 Volume +

17 Volume -

18 Brightness +

19 Brightness -

20 Color saturation +

21 Color saturation -

22 Bass +

23 Bass -

24 Treble +

25 Treble -

26 Balance right

27 Balance left

63 System select


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Table 3. RC5 TV instructions

TV Instruction Description

10 1/2/3 digits / 10

11 Freq./prog./ch./11

12 Standby

13 Mute/de-mute

14 Personal pref.

15 Display

28 Contrast +

29 Contrast -

30 Search +

31 Tint/hue -

32 Ch./Prog. +

33 Ch./Prog. -

36 Spatial stereo

37 Stereo/mono

38 Sleep timer

39 Tint/hue. +

40 RF switch

41 Store/execute/vote

42 Time

43 Scan fwd./increment.

44 Decrement

46 Sec con/menu

47 Show clock

48 Pause

49 Erase/correct

50 Rewind

51 Go to

52 Wind

53 Play

54 Stop

55 Record

56 External 1

57 External 2

59 Advance

60 TXT sub-mode/12


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61 Sys. Standby

62 Crispener

Table 3. RC5 TV instructions (continued)

TV Instruction Description


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2.4 Bit descriptionsRC5 bits are Manchester coded, this means that a bit is composed of 2 alternated half bits. A low to high transition means that the bit is "1", a high to low transition means "0".

The frequency used to code a bit is 562.429 Hz (1778 µs), half bits have the same width (889 µs each).

Figure 6. RC5 bit description

2.5 RC5 frames RC5 frames are composed of 14 bits, the width of a frame is 24.892 ms (14 x 1.778 ms = 24.892 ms)

To avoid frame collisions, an idle time is inserted between two frames with a specific width. The idle time is defined as 50 bits wide. So the periodicity of a frame is 64 x 1 bit width: 64 x 1.778 = 113.792 ms (exactly 113.788 ms).

Figure 7. RC5 frame description

"0"

889 µs

1778 µs

14 bits50 bits14 bits

Frame 1 Idle time Frame 2

64 bits = 113.788 ms


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2.6 RC5 carrier frequencyThe RC5 carrier frequency is 36 kHz. To minimize the power consumption, the duty cycle used for a pulse is fixed at 25%, so the width of a pulse is 6.94 µs.

Figure 8. RC5 carrier frequency description

1 1 0 0

6.94 μs 20.82 μs

Carrier frequencyFrequency = 36 kHzDuty Cycle = 25%

Main Signal to send:Manchester coded

Software description AN2957

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3 Software description

3.1 IntroductionThe software provided with this application note enables the user to send all RC5 instructions to all RC5 receiver devices. It contains an RC5 driver with functions and software flags.

The software is designed to avoid frame collisions; an idle time is inserted between two frames with a specific width (50 bits).

The application uses 5 peripherals:

● IRTIM: (IR interface with timers) generates the IR signal using TIM2 and TIM3

● TIM2: (Timer2) provides the Carrier signal with a frequency of 36 kHz

● TIM3: (Timer3) provides the main signal to be sent (RC5 Frame)

● GPIO: (General purpose I/O) provides the I/O to be connected to the buttons of the the remote control

● CLK: (Clock controller) enables the clocks and provides the correct clock frequency for the timers

AN2957 Software description

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Figure 9. Application architecture and description

main c

ApplicationLayer

RC5 softwareLayerrc5.h

rc5.c

stm8l10x.h

stm8l10x_conf.hstm8l10x_it.h

stm8l10x_it.c

stm8l10x_tim3.c

stm8l10x_tim3.h

stm8l10x_tim2.

stm8l10x_tim2.h stm8l10x_irtim.h

stm8l10x_irtim.c

stm8l10x_clk.h

stm8l10x_clk.c stm8l10x_gpio.c

stm8l10x_gpio.h

API Layer

FW Drivers

HardwareLayer

STM8L 10xmicrocontroller


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3.2 RC5 functionsRC5_BinFrameGeneration function

Generates and returns a binary format of the RC5 frame: the flowchart of this function is described below

uint16_t RC5_BinFrameGeneration ( RC5_Address_TypeDef RC5_Address,

RC5_Instruction_TypeDef RC5_Instruction,

RC5_Ctrl_TypeDef RC5_Ctrl)

RC5_ManchesterConvert function

Converts an RC5 binary format Frame to a RC5 Manchester format frame.

uint32_t RC5_ManchesterConvert (uint16_t RC5_BinaryFrameFormat)

RC5_SendFrame function

Sends a Manchester Format RC5 Frame.

void RC5_SendFrame(uint32_t RC5_ManchesterFrameFormat)

RC5_CtrlBitReverse function

Reverses the state of the RC5 Control bit (can be used to determine whether a button is pressed and held down, or pressed and released continuously).

RC5_Ctrl_TypeDef RC5_CtrlBitReverse(RC5_Ctrl_TypeDef RC5_Ctrl);

3.3 RC5 flags

Table 4. RC5 flags

Flag name Flag description

Send_Operation_Completed Flag 0: The RC5 frame is not completely sent

1: The RC5 frame is completely sent

Send_Operation_Ready Flag 0: The RC5 frame is not yet ready to be send

1: The RC5 frame is ready to be send


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3.4 Application flowcharts

Figure 10. Main loop flowchart

Identify which key is pressedand send the corresponding

RC5 data

If key is pressed

Enable and configure IRTIMto generate IR signal

Enable and configure TIM3 to generate a periodic interrupt T = 889 µs

and enable the TIM3 Update Interrupt

Enable and configure TIM2 to generate the carrier signal

Frequency = 36 kHzPWM Duty cycle = 25%

Start

No

Yes

INTERRUPT


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Figure 11. Send frame function flowchart

End

Enable Interrupts

Set the Send_Operation_Ready flag to indicate that the frame is ready to be sent

Convert the frame to the Manchester format

Disable Interrupts

Generate a binary format of the Frame

Begin SendFrame


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Figure 12. RC5 SendFrame function flowchart (this function is called during the TIM3 Update Interrupt routine)

BeginRC5_SendFrame

If Flag Send Operation Ready =1

Yes

No

No

NoYes

Yes

If all bits of the Manchesterformat frame are sent

Clear FlagSend_operation_completed = 0

If the bit to be sent is 1

Force the TIM3Ch1 Output to 1

Force the TIM3Ch1 Output to 0

Increment BitsSent_Counter(BitsSent_Counter++)

Set FlagSend_Operation_Completed = 1

Reset BitsSent_Counter(BitsSent_Counter = 0)

Force the TIM3 Ch1 Output to 0

End

Application description AN2957

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4 Application description

This Application note is provided with a basic application in which only two keys are used for remote control:

● Button 1 (PA5) enables user to send "VolumeUp" RC5 Instruction to "TV1" (Key button on STM8L1X-EVAL Board).

● Button 2 (PD7) enables user to send "VolumeDown" RC5 Instruction to "TV1" (Joystick Select button on STM8L1X-EVAL Board).

However, user can implement a bigger remote control to fit its application needs.

Figure 13. Simplified RC5 transmitter

STM8L10x

Button 2 Button 1

PD7 PA5

PA0NOT

IR Led

GND

AN2957 Hardware description

Doc ID 15550 Rev 2 19/21

5 Hardware description

Figure 14. RC5 transmitter

RC5 remote control

GND

IR Led

R2=100

VCC

R1=10K

Port B Port D

STM8L 10x

Revision history AN2957

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6 Revision history

Table 5. Document revision history

Date Revision Changes

23-Apr-2009 1 Initial release.

04-Jun-2010 2

Removed several common instructions (from 71 to 124) in Table 2: RC5 common instructions on page 7Removed several TV instructions (from 70 to 127) in Table 3: RC5 TV instructions on page 8

AN2957

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