2002 Microchip Technology Inc. DS00236A-page 5
AN236
120 kHz Carrier Generator
X-10 uses 120 kHz modulation to transmit information
over 60 Hz power lines. It is possible to generate the
120 kHz carrier with an external oscillator circuit. A sin-
gle I/O pin would be used to enable or disable the oscil-
lator circuit output. However, an external oscillator
circuit can be avoided by using one of the PICmicro
MCU’s CCP modules.
The CCP1 module is used in PWM mode to produce a
120 kHz square-wave with a duty cycle of 50%.
Because X-10 specifies the carrier frequency at
120 kHz (+/- 2 kHz), the system oscillator is chosen to
be 7.680 MHz, in order for the CCP to generate pre-
cisely 120 kHz. Calculations for setting the PWM
period and duty cycle are shown in the code listing
comments for the function InitPWM.
After initialization, CCP1 is continuously enabled, and
the TRISC bit for the pin is used to gate the PWM out-
put. When the TRISC bit is set, the pin is an input and
the 120 kHz signal is not presented to the pin. When
the TRISC bit is clear, the pin becomes an output and
the 120 kHz signal is coupled to the AC power line
through a transistor amplifier and capacitor, as
depicted in Figure 5.
Since the impedance of a capacitor is Zc = 1/(2*π*f*C),
a 0.1 µF capacitor presents a low impedance to the
120 kHz carrier frequency, but a high impedance to the
60 Hz power line frequency. This high-pass filter allows
the 120 kHz signal to be safely coupled to the 60 Hz
power line, and it doubles as the first stage of the
120 kHz carrier detector, described in the previous
section.
To be compatible with other X-10 receivers, the maxi-
mum delay from the zero-crossing to the beginning of
the X-10 envelope should be about 300 µs. Since the
zero-crossing detector has a maximum delay of
approximately 64 µs, the firmware must take less than
236 µs after detection of the zero-crossing to begin
transmission of the 120 kHz envelope.
Transformerless Power Supply
The PIC16F877A and other board circuits require a 5V
supply. In this application, the X-10 controller must also
transmit and receive its data over the AC line. Since
X-10 components are intended to be plugged into a
wall outlet and have a small form factor, a transformer-
less power supply is used. Two characteristics of trans-
formerless supplies that should be kept in mind are
limited current capacity, and lack of isolation from the
AC mains (see the warning note)!
Figure 6 illustrates the transformerless power supply
used in this application. To protect the circuit from
spikes on the AC power line, a 130V VDR (voltage
dependent resistor) is connected between Line and
Neutral. A Positive Temperature Coefficient (PTC)
device acts as a resettable fuse, which limits current
between Ground and Neutral. The 47Ω resistor limits
current into the circuit, and the 1 MΩ resistor provides
a discharge path for the voltage left on the capacitor
when the circuit is unplugged from the wall. Two diodes
rectify the voltage across the 1000 µF capacitor and
5.1V Zener diode to produce a 5V supply.
The reader may wish to refer to the technical brief
TB008, “Transformerless Power Supply”, available for
download from the Microchip web site, for additional
information on transformerless power supply design.
FIGURE 5: 120 kHz CARRIER GENERATOR
WARNING: This circuit is not isolated from 120 VAC.
Act with caution when constructing or using such a
circuit, and ensure that it is contained within a suitable
insulated enclosure. Follow isolation precautions to
avoid personal injury or damage to test equipment
and development tools.
0.1 µF
X2 Rated
High-Pass Filter
1 M
Ω
7.680 MHz
PIC16F87XA
RC3/CCP
+5 VDC
120 VAC
50Ω
200Ω
OSC1
OSC2
AN236
DS00236A-page 6 2002 Microchip Technology Inc.
FIGURE 6: TRANSFORMERLESS POWER SUPPLY
Load Switch
A load switch is included on the home controller so that
it may act as a lamp module, with its own house and
unit address. A Triac was selected as the load switch,
because its medium power switching capacity and
rapid switching capability make it well-suited for lamp
control and dimming.
A Triac is an inexpensive, three-terminal device that
basically acts as a high speed, bi-directional AC switch.
Two terminals, MT1 and MT2, are wired in series with
the load. A small trigger current between the gate and
MT1 allow conduction to occur between MT1 and MT2.
Current continues to flow after the gate current is
removed, as long as the load current exceeds the latch-
ing value. Because of this, the Triac will automatically
switch off near each zero-crossing as the AC voltage
falls below the latching voltage.
A Teccor
®
L4008L6 Triac was selected because it has
a sensitive gate that can be directly controlled from the
logic level output of the PICmicro MCU I/O pin. The
sensitive gate Triac can control AC current in both
directions through the device, even though the
PICmicro MCU can provide only positive voltages to
the gate.
A variable dimmer is created by including a delay
between the time of each zero-crossing and the time
that the trigger current is provided to the Triac from the
PICmicro MCU.
The design and control of a lamp dimmer using a
PICmicro MCU is discussed in detail in PICREF-4
Reference Design, “PICDIM Lamp Dimmer for the
PIC12C508”.
FIGURE 7: LOAD SWITCH/DIMMER (TRIAC)
2.25 µF
2.25 µF
5.1V Zener
1000 µF
1.1M
LN
G
+5 VDC
PTC
1N4005
1N4005
VDR
PIC16F87XA
RA5
120 VAC Out
120 VAC In
L4008L6
VSS
Return Hot
Gate
MT1
MT2
1N4148470Ω
2002 Microchip Technology Inc. DS00236A-page 7
AN236
LCD Module
The 2-line x 16-character display uses the HD44780U
Display Controller. Eight data lines and three control
lines are used to interface to the PICmicro MCU. If
fewer I/O pins are available, the LCD can be operated
in Nibble mode using only four data lines, with some
additional software overhead. A basic LCD library is
included in this application, which provides the
necessary functions for controlling this type of LCD.
Real-Time Clock
A real-time clock is implemented using Timer1. The
real-time clock keeps track of the present time using a
routine called UpdateClock. It also determines the
rate that the buttons are read by a routine called
ScanKeys.
Timer1 is set to cause an interrupt each time it
overflows. By adding a specific offset to Timer1 each
time it overflows, the time before the next overflow can
be precisely controlled. The button reading routine,
ScanKeys, is called each time a Timer1 interrupt
occurs. Since ScanKeys performs debouncing of the
button presses, a suitable rate to check the buttons is
once every 25 ms.
With a 32 kHz crystal, the counter increments once
every 31.25 µs when the prescaler is set to 1:1. In order
for Timer1 to generate an interrupt once every 25 ms,
TMR1H:TMR1L are pre-loaded with 0xFCE0h.
The Timer1 interrupt interval, or tick, can be seen in the
following equation:
(FFFFh – FCE0h)*1/32 kHz = .025 s = 1 tick
Each time ScanKeys is called (every 25 ms), it calls
UpdateClock. UpdateClock keeps track of the time
unit variables: ticks, seconds, minutes, and hours.
Since every 25 ms equals one tick, seconds are incre-
mented every 40 ticks. Minutes and hours are
incremented in a similar fashion.
Push Buttons
Five push buttons, connected to RB1-RB5, are used for
user interaction with the application. Each normally open
push button will pull a port pin low when it is pressed.
Light Sensor
To detect the ambient light level, a CdS photoresistor is
used in conjunction with an 820Ω resistor to create a
voltage divider. The voltage on the divider varies with
the intensity of ambient light and is connected to an
analog channel (AN0) of the microcontroller.
In-Circuit Debugger
RB6 and RB7 have been reserved for In-Circuit Serial
Programming
TM
(ICSP
TM
) and the in-circuit debugger
(ICD). However, do not connect the ICD or any other
development tool, without taking first isolating the
entire application from wall power (see the previous
warning notes)!
Control Data Storage
Certain control data that is programmable by the user
must be stored in non-volatile memory. The PICmicro
MCU’s built-in EEPROM is well-suited to this task.
To use EEPROM memory space most efficiently (by
avoiding wasted bits), on/off times and light sensor
control flags are stored using the format shown in
Figure 8. Figure 9 shows the location of on/off times
and other information within the data EEPROM. Using
this data organization, only 48 bytes of EEPROM are
required to store the on/off times and light sensor
control flags for 16 units.
FIGURE 8: ON/OFF TIME STORAGE
FIGURE 9: EEPROM DATA
Each time that minutes are incremented within the
UpdateClock routine, a flag is set that enables a rou-
tine called CheckOnOffTimes to be called from the
main loop. CheckOnOffTimes compares the present
time with the unit on and off times stored in EEPROM
memory. If there is a match, then a flag is set to either
turn the unit on or off, by sending it the appropriate X-10
command when the routine ControlX10Units is
called.
A = AM/PM bit for On Hour
C = AM/PM bit for Off Hour
B = Control bit for On at Dusk
D = Control bit for Off at Dawn
On Hour Off Hour
EEHours
BOnMin
EEOnMinutes
A
C D
Off Min
EEOffMinutes
4 bits 4 bits
6 bits
6 bits
11
11
OnHour OffHour
Unit 1
OnHour OffHour
OnHour OffHour
Unit 2
Unit 3
0x010
0x011
0x012
0x001
0x002
House Address
Unit Address
System
System
B OnMinA
B OnMinA
B OnMinA
Unit 1
Unit 2
Unit 3
0x020
0x021
0x022
B OffMinA
B OffMinA
B OffMinA
Unit 1
Unit 2
Unit 3
0x030
0x031
0x032
Address Unit
Data
AN236
DS00236A-page 8 2002 Microchip Technology Inc.
APPLICATION FIRMWARE
OVERVIEW
The firmware is divided into several different files to
facilitate adaptation of the code to other applications.
Following is a summary of the files associated with this
application note:
• x10lib.asm Defines X-10 functions.
• x10lib.inc Defines X-10 constants and
macros.
• x10hc.asm Main application code for the
home controller.
• x10demo.asm Example code that shows how
to use the X-10 library macros.
• lcd.asm Defines the routines necessary
for driving the LCD.
• p16f877A.lkr Standard linker file for
PIC16F877A parts.
• p16f877A.inc Standard include file for
PIC16F877A parts.
Detailed descriptions of operation can be found in the
comments within the code listing. The X-10 library
functions and macros are described in the next section.
X-10 LIBRARY
A simple library of commands was developed and used
for the home controller. It can be used with little or no
modification in a user’s application. The library consists
of two files: x10lib.asm and x10lib.inc.
To use the library, a user need only understand the
function of the macros defined in x10lib.inc. The
macros greatly simplify the use of the library by elimi-
nating the need for the user to understand every X-10
function in x10lib.asm. Examples of how the macros
are used are included in the file x10demo.asm.
The macros are explained below:
InitX10
This macro is used to initialize the peripherals that pro-
vide X-10 functionality. It must be called in the applica-
tion program before any of the below macros will work.
It is used as follows:
InitX10
SkipIfTxReady
Before sending an X-10 message, it is necessary to
make sure that another message is not already being
sent, which is signified by the X10TxFlag being set.
This macro simply checks that flag and skips the next
instruction if it is okay to begin a new transmission.
Otherwise, there is a chance that a new transmission
will interrupt an ongoing transmission.
It is used as follows:
SkipIfTxDone
GOTO $-1 ;loop until ready to
;transmit next message
SendX10Address (House, Unit)
This macro is used to send an X-10 address for a par-
ticular unit. It requires two arguments, a house address
and unit address. The definitions for all house and unit
addresses are defined in x10lib.inc. To use this
macro to send the address for unit 16 at house P, one
simply types:
SendX10Address HouseP, Unit16
SendX10AddressVar
This macro is used to send an X-10 address, defined
by variables rather than constants. To send an address
contained in the user variables MyHouse and MyUnit,
the following sequence would be applied:
MOVF MyHouse, W ;contains a value
;from 0-16
MOVWF TxHouse
MOVF MyUnit, W ;contains a value
;from 0-16
MOVWF TxUnit
SendX10AddressVar
2002 Microchip Technology Inc. DS00236A-page 9
AN236
SendX10Command (House, Function)
This macro is used to send an X-10 command. It
requires two arguments, the house address and func-
tion code. The definitions for all house addresses and
function codes are defined in x10lib.inc. To use this
macro to send the command ‘All Lights On’ to all units
at house A, one types:
SendX10Command HouseA, AllLightsOn
SendX10CommandVar
This macro is used to send an X-10 command, defined
by a variable rather than a constant. To use this macro
to send the command stored in the user variable
MyCommand to all units at MyHouse, one types:
MOVF MyHouse, W ;contains a value
;from 0-16
MOVWF TxHouse
MOVF MyCommand, W ;any X-10
;function
;defined in
;x10lib.inc
MOVWF TxFunction
SendX10CommandVar
SkipIfRxDone
Before reading an X-10 message, it is necessary to
make sure that a complete message has been
received. This is signified by the X10RxFlag being set.
This macro simply checks that flag and skips the next
instruction if a new X-10 message has been received.
It is used as follows:
SkipIfRxDone
GOTO $-1 ;loop until message
;received
SkipIfAddressRcvd
It may be necessary to make sure that an address was
received by using this macro, which checks to see if the
RxCommandFlag is clear.
It is used as follows:
SkipIfAddressRcvd
GOTO $-1 ;loop until address
;received
SkipIfCommandRcvd
Or, it may be necessary to make sure that a command
was received by using this macro, which checks to see
if the RxCommandFlag is set.
It is used as follows:
SkipIfCommandRcvd
GOTO $-1 ;loop until command
;received
ReadX10Message
This macro is called to read a received X-10 message,
which may be either an address or a command. If the
message was an address, then the received house and
unit codes will be stored in the variables RxHouse and
RxUnit, respectively. If the message was a command,
then the received house address and function code will
be stored in the variables RxHouse and RxFunction.
It is simply called as follows:
ReadX10Message
Please refer to the example code in x10demo.asm to
see how each of these macros is used in a simple
application.
AN236
DS00236A-page 10 2002 Microchip Technology Inc.
Memory Usage
Memory usage for the X-10 portion of the application is
summarized in Table 2.
TABLE 2: SUMMARY OF MEMORY USAGE FOR X-10 FUNCTIONALITY
Memory usage for the entire home controller
application is summarized in Table 3.
TABLE 3: SUMMARY OF MEMORY USAGE FOR THE HOME CONTROLLER
Memory Type Used Available on PIC16F877A Percent Used
FLASH Program Memory 437 words 8453 words 5%
Data Memory (RAM) 62 bytes 368 bytes 17%
EEPROM Data Memory 0 bytes 256 bytes 0%
Memory Type Used Available on PIC16F877A Percent Used
FLASH Program Memory 3762 words 8453 words 44.5%
Data Memory (RAM) 168 bytes 368 bytes 45.6%
EEPROM Data Memory 51 bytes 256 bytes 20%
2002 Microchip Technology Inc. DS00236A-page 11
AN236
CONCLUSION
The PICmicro MCU is well-suited to X-10 applications.
With its plethora of on-chip peripherals and a few exter-
nal components, a PICmicro MCU can be used to
implement an X-10 system that can transmit and
receive messages over the AC power line wiring. The
small code size of the X-10 library leaves ample space
for the user to create application specific code.
PICmicro MCUs, such as the PIC16F877A, have plenty
of additional resources for creating more complex X-10
applications, while smaller PICmicro MCUs can be
selected for economical use in simpler X-10
applications.
USEFUL WEB REFERENCES
• http://www.abacuselectrics.com/x10.htm
This web site describes how to build an appliance
module that utilizes the PIC16C52 or PIC16F84.
Parts of this project’s receiver circuit, designed by
Phil Plunkett, were adapted to the home controller
application.
• http://www.microchip.com
The Microchip web site features data sheets, product
information, and more. Helpful technical
documentation available here include:
AN521 “Interfacing to AC Power Lines”
TB008 “Transformerless Power Supply”
PICREF-4 “PICDIM Lamp Dimmer for the
PIC12C508”
• http://www.x10.com/support
The X10 Wireless Technology, Inc.
TM
web site fea-
tures technical information and FAQs pertaining to
the X-10 communication protocol.
AN236
DS00236A-page 12 2002 Microchip Technology Inc.
APPENDIX A: HOW DOES THE X-10
PROTOCOL WORK?
X-10 transmissions are synchronized with the
zero-crossings on the AC power line. By monitoring for
the zero-crossings, X-10 devices know when to trans-
mit or receive X-10 information. A binary ‘1’ is repre-
sented by a 1 ms long burst of 120 kHz, near the
zero-crossing point of the AC. A binary zero is
represented by the lack of the 120 kHz burst.
FIGURE A-1: X-10 TRANSMISSION TIMING
A complete X-10 message is composed of a start code
(1110), followed by a house code, followed by a key
code. The key code may be either a unit address or a
function code, depending on whether the message is
an address or a command. Table A-1 and Table A-2
show the possible values of the house and key codes.
60 Hz
120 kHz
1 ms
2.778 ms
5.556 ms
8.333 ms
Note 1: These 120 kHz carrier bursts are timed to coincide with the zero-crossing of the other phases,
when implemented.
(1)
(1)
(1)
(1)
2002 Microchip Technology Inc. DS00236A-page 13
AN236
TABLE A-1: HOUSE CODES
TABLE A-2: KEY CODES
When transmitting the codes in Table A-1 and
Table A-2, two zero-crossings are used to transmit
each bit as complementary bit pairs (i.e., a zero is rep-
resented by 0-1, and a one is represented by 1-0). For
example, in order to send the house code A, the four-bit
code in Table A-1 is 0110, and the code transmitted as
complimentary bit pairs is 01101001. Since house and
key codes are sent using the complimentary format, the
start code is the only place where the pattern 1110 will
appear in an X-10 data stream.
The key code, which is 5-bits long in Table A-2, takes
10 bits to represent in the complimentary format.
Because the last bit of the key code is always zero for
a unit address and one for a function code, the last bit
of the key code can be treated as a suffix that denotes
whether the key code is a unit address or function
code.
A complete block of data consists of the start code,
house code, key code and suffix. Each data block is
sent twice, with 3 power line cycles, or six
zero-crossings, between each pair of data blocks.
For example, to turn on an X-10 module assigned to
house code A, unit 2, the following data stream would
be sent on the power line, one bit per zero-crossing.
First, send the address twice:
Next, wait for three cycles (six zero-crossings):
Then, send the command twice:
Lastly, wait for three cycles (six zero-crossings) before
sending the next block:
There are exceptions to this format. For example, the
bright and dim codes do not require the 3-cycle wait
between consecutive dim commands or consecutive
bright commands. For a complete discussion of all
X-10 messages, please refer to the X10 Wireless
Technology, Inc. web site (see the "USEFUL WEB
REFERENCES" section).
House
Addresses
House Codes
H1 H2 H4 H8
A 0110
B 1110
C 0010
D 1010
E 0001
F 1001
G 0101
H 1101
I 0111
J 1111
K 0011
L 1011
M 0000
N 1000
O 0100
P 1100
Unit Addresses
Key Codes
D1 D2 D4 D8 D16
1 01100
2 11100
3 00100
4 10100
5 00010
6 10010
7 01010
8 11010
9 01110
10 11110
11 00110
12 10110
13 00000
14 10000
15 01000
16 11000
Function Codes
All Units Off 00001
All Units On 00011
On 00101
Off 00111
Dim 01001
Bright 01011
All Lights Off 01101
Extended Code 01111
Hail Request 10001
Hail Acknowledge 10011
Pre-set Dim 101X1
Extended Code
(Analog)
11001
Status = On 11011
Status = Off 11101
Status Request 11111
1110 01101001 10101001 01
START HOUSE A UNIT 2 Suffix
1110 01101001 10101001 01
START HOUSE A UNIT 2 Suffix
000000
1110 01101001 01011001 10
START HOUSE A ON Suffix
1110 01101001 01011001 10
START HOUSE A ON Suffix
000000
AN236
DS00236A-page 14 2002 Microchip Technology Inc.
APPENDIX B: HOME CONTROLLER
OPERATING
INSTRUCTIONS
Welcome Screen
The home controller user interface consists of five but-
tons and a 2 x 16 LCD. Upon power-up, the Welcome
screen is displayed. This screen displays a welcome
message and the time. Immediately, the seconds begin
incrementing and the PICmicro MCU begins keeping
track of the time.
Figure B-1 shows the Welcome screen and the location
and functionality of each button. Depending on the
screen viewed, each of the five buttons performs a
different function.
When the Welcome screen is displayed, the buttons
enable access to the following functions:
•Press menu to enter the Select Function screen.
•Press up to brighten the lamp that is plugged into
the home controller.
•Press down to dim the lamp.
•Press enter to turn the lamp on.
•Press exit to turn the lamp off.
FIGURE B-1: WELCOME SCREEN
Select Function Screen
When viewing the Welcome screen, the menu button
enables access to the Select Function screen. Each
successive press of the menu button cycles through
the four main functions of the user interface: setting the
system time, setting the system address, setting the
light sensor, or programming the unit on and off times,
as illustrated in Figure B-2.
FIGURE B-2: SELECT FUNCTION
SCREENS
Set System Time Screen
Use the Set System Time screen to set the time.
SETTING SYSTEM TIME
1. Starting from the Welcome screen, press menu
until the Set System Time screen is displayed
and press enter.
2. Press up/down to set the hours.
3. Press enter when the correct hour, including AM
or PM, has been selected.
4. Repeat this process to set the minutes.
5. If the time is correct, select Y (the default) using
the up/down buttons and press enter. This
returns to the Welcome screen with the new
time displayed.
6. If the time is not correct, select N and press
enter. This will return the user to step 2 so the
correct time can be entered.
7. Press exit at any time to return the user to the
Welcome screen without saving the new time.
FIGURE B-3: SET SYSTEM TIME SCREENS
Welcome Home
12:00:00 AM
menu up down
enter
exit
1
2
3
4
menu up down
enter
exit
menu up down
enter
exit
menu up down
enter
exit
menu up down
enter
exit
Select Function
Program Unit
Select Function
Set Light Sensor
Select Function
Set System Addr
Select Function
Set System Time
menu up down
enter
exit
menu up down
enter
exit
1
2
menu up down
enter
3
exit
Set System Time
12:00 AM Set hrs
Set System Time
12:00 AM Set min
Set System Time
12:00 AM Okay? Y
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