AN239

AN239
Bit Banged LIN Slave Node for PIC16 & PIC18
Author:
Ross Fosler
Microchip Technology Inc.
INTRODUCTION
The Local Interconnect Network (LIN), as described in
the LIN v1.2 specification, is a multi-layered system. The
levels vary from the physical interface up to the high
level application. This application note focuses on the
implementation of a low level driver, essentially an interface between the physical hardware connection and the
higher level application firmware. Specifically, this application note presents a generic ‘bit banged’ LIN slave
driver for both the PIC16 and PIC18 family of PICmicro®
microcontrollers.
There are many details to this firmware design; however, this application note focuses mainly on how to set
up and use the driver. Therefore, the LIN system
designer should be able to get an application running
on LIN quickly without spending significant time on the
details of LIN.
Some information about the firmware design is provided at the end of this document for the curious
designer who wants to learn a little more about LIN and
this driver implementation.
The reader should note information in this application
note is presented with the assumption that the reader
is familiar with LIN specification v1.2, the most current
specification available at the time this document was
written. Therefore, not all details about LIN are discussed. Refer to the References section for additional
information.
APPLICATIONS
The first question that must be asked is: “Will this driver
work for my application?” The next few sections can
help those who would like to know the answer to this
question and quickly decide whether this is the appropriate driver implementation for their application. The
important elements that have significant weight on the
decision include available process time, resource
usage, and bit rate performance.
 2002 Microchip Technology Inc.
Process Time
Available process time is dictated predominately by bit
rate, clock frequency, and code execution. Since code
execution varies depending on the state within the LIN
driver and there being many states, generating a single
equation for process time is unrealistic. A much simpler
solution is to test the process time. Figure 1 shows the
approximate average available process time for a node
running at 8 MHz.
FIGURE 1:
AVAILABLE PROCESS TIME
@ 8 MHz
80%
70%
50%
4.8K
9.6K
19.2K
When the LIN bus is IDLE, the driver uses significantly
less process time. Although dependent on the same
conditions stated above, the used process time is
extremely low. At 8 MHz, the average available
process time is greater than 98%.
Resource Usage
A few of the hardware resources are used to maintain
robust communications and precise timing. Timer0 is
used for maintaining communications timing and bus
activity time. In addition, the timer prescaler is adjusted
under various conditions to simplify the code and
improve performance in many states of the driver. An
external interrupt is used for START edge detection for
each received byte; either an interrupt-on-change pin,
or the INT pin can be configured as the interrupt
source.
DS00239A-page 1
AN239
Bit Rate
In summary, this basically means the PIC16 and PIC18
bit banged drivers are well suited for applications that
do not require excessive firmware processing and tight
timing. There are a number of peripherals available for
the PIC16 and PIC18 devices that can enhance the
application without extensive firmware. Some of these
include A/D, PWM, USART, and comparators. Also, the
PIC18 devices do have an advantage in that they have
an extra interrupt vector and hardware stack management capability. Some applications could include motor
control, sensor feedback, on/off control, and indication.
By selecting the appropriate clock frequency, the driver
is designed to operate over the specified operating
range of LIN: 1000 bps to 20000 bps. Note, however,
that the clock must be selected such that at least 70
instructions can be executed per every bit received.
Refer to Figure 2 for recommended operating regions.
Summary
The driver is designed almost entirely in firmware. Only
the hardware peripherals standard to PIC16 and PIC18
MCUs are used. Thus, all communications and timing
required by the LIN specification are controlled in firmware. This implies a certain percentage of software
resources are consumed, most importantly, time. To
put this into perspective, at 19.2 Kbps using an 8 MHz
oscillator source, an average of 50% of the process
time is used by the driver. Also, given the intolerance to
uncertainty, interrupts (high priority for PIC18) should
be restricted to the LIN communications driver when
the instruction rate to bit rate ration (FOSC/B) is small
(i.e., less than 200). For PIC18 devices, the low priority
interrupt vector is available since low priority interrupts
do not interfere with high priority interrupts.
FIGURE 2:
RECOMMENDED OPERATING REGIONS
Clock Frequency
6 MHz
HS Mode Operation(1)
4 MHz
XT, and INTRC(1)
No Operation
2 MHz
1.2k
7.2k
Bit Rate
14k
20k
Note 1: Check specific device for available Oscillator modes.
DS00239A-page 2
 2002 Microchip Technology Inc.
AN239
SETTING UP
FIGURE 3:
PROJECT SETUP
Now that the decision has been made to use this driver,
it is time to setup the firmware and start building an
application. For an example, a complete application,
referenced in the appendixes for both the PIC16 and
PIC18 families, is built with the LIN driver.
Here are the basic steps required to set up your project:
1.
Setup a project in MPLAB® IDE. Make sure you
have the important driver files included in your
project:
serial.asm, lin.asm, and linevent.asm.
2.
3.
4.
5.
Include a main entry point in your project:
main.asm. Edit this file as required for the application. Make sure that the interrupt is setup correctly and initialize the driver. Also ensure any
external symbols are included.
Edit linevent.asm to respond to the appropriate IDs. This could be a table or some simple
compare logic. Be certain to include any
externally defined symbols.
Add any additional application related modules.
The example uses idxx.asm for application
related functions related to specific IDs.
Edit the lin.def file to set up the compile time
definitions of the driver. The definitions
determine how the driver functions.
The Project
The first step is to setup the project. Figure 3 shows an
example of what the MPLAB project setup should look
like. The following files are required for the LIN driver to
operate:
•
•
•
•
•
lin.lkr - Linker script file
main.asm - Main entry point into the program
serial.asm - Serial communications engine
lin.asm - LIN driver
linevent.asm - LIN event handling table
Any additional files are defined by the system designer
for the specific application. For example, Figure 3
shows these files labeled as idxx.asm, where xx represents the LIN ID number. This is simply a programming style that separates ID handling into individual
objects thus making the project format easier to understand. Other objects could be added and executed
through the main module, main.asm, and the event
handler.
The Main Object
The main.asm module contains the entry point into the
program, which is where the driver, hardware, and variables should be initialized. To initialize the driver, call
the l_init function. The firmware referenced in
Appendix B demonstrates this.
Also included in this module is the interrupt vector. The
serial function is interrupt based; therefore, it must be
included at the interrupt vector. The following code
demonstrates this for use with PIC16 MCUs.
EXAMPLE 1:
INTERRUPT VECTOR
CODE EXAMPLE
_INTERRUPT_V
CODE 0x0004
InterruptHandler
movwf
W_TEMP
;Save
swapf
STATUS, W
clrf
STATUS
movwf
STATUS_TEMP
call
SerialEngine
swapf
movwf
swapf
swapf
STATUS_TEMP, W ;Restore
STATUS
W_TEMP, F
W_TEMP, W
retfie
 2002 Microchip Technology Inc.
DS00239A-page 3
AN239
The above example could also be used for PIC18
MCUs; however, PIC18 MCUs have the Fast Register
Stack and a different interrupt vector. If the fast register
stack is used, then time and space could be saved by
eliminating the context save and restore.
Definitions
There are numerous compile time definitions, all of
them located in lin.def, that are used to setup the
system. Table 1 lists and describes these definitions.
Likewise, the definitions are also listed in Appendix A.
Only five of these definitions are critical for getting a
system running. They are:
•
•
•
•
•
MAX_BIT_TIME
NOM_BIT_TIME
MIN_BIT_TIME
USE_GP_CHANGE
RX_ADVANCE (or RX_DELAY)
The first three definitions, the bit time definitions, setup
the baud rate and its boundary for communication. The
next item depends on the application hardware design.
The LIN designer needs to setup an external START
edge detection source; the two options are the INT pin
or an interrupt-on-change pin. The last, yet very important definition, is the receive advance or delay. The
receive advance (or delay) is used to advance (or
delay) the time-base to align to the center of the next bit
after the START bit.
DS00239A-page 4
LIN Events
LIN event functions are where the ID is decoded to
determine what to do next, transmit, receive, and how
much. The designer should edit or modify the event
function to handle specific LIN IDs (see Appendix B for
an example). One possibility is to set up a jump table.
Another option is to set up some simple compare logic.
The example firmware uses simple compare logic.
ID Modules
The application firmware must be developed somewhere in the project, it can be in main or in separate
modules; however, from a functional perspective, it
does not matter. The example firmware uses separate
ID modules for individual handling of IDs and their
associated functions. The most important part is to
remember to include all the external symbols that are
used. The symbols used by the driver are in lin.inc;
this should be included in every application module.
 2002 Microchip Technology Inc.
AN239
TABLE 1:
COMPILE TIME DEFINITIONS
Definition Name
Value
Description
d'11'
Sets the receive break threshold. For low tolerance oscillator sources, this value
should be ‘11’, for high tolerance sources, this value should be ‘9’.
LIN_ACTVE_TIME_PS
b'10001000'
The value loaded into the option register when the slave is actively receiving or
transmitting on the LIN bus. A prescale value of 1x is ideal for bit rates between
4800 bps and 14400 bps at 4 MHz.
LIN_IDLE_TIME_PS
b'10010110'
The value loaded into the option register when the LIN bus is IDLE. A prescale
setting of 128x is the desired choice for the prescaler.
LIN_SYNC_TIME_PS
b'10010010'
The value loaded into the option register when the slave is capturing the sync byte. A
prescale setting of 8x is the desired choice for the prescaler.
BRK_THRESHOLD
MAX_BIT_TIME
d'118'
The upper boundary bit time for synchronization, which should equal
((FOSC x 1.15) / 4) /(bit rate) – 2
d'39'
The maximum allowable time for the header. This value equals ((34 + 1) x 1.4) – 10,
and should not be changed unless debugging.
MAX_IDLE_TIME
d'195'
Defines the maximum bus IDLE time; the spec defines this to be 25000 bit times.
The value equals 25000 / 128. The 128 comes from the LIN_IDLE_TIME_PS definition.
MAX_TIME_OUT
d'128'
Specifies the maximum time-out between wake-up requests. The LIN specification
defines this to be 128 bit times.
MIN_BIT_TIME
d'87'
NOM_BIT_TIME
d'102'
MAX_HEADER_TIME
RC_OSC
N/A
The lower boundary bit time for synchronization, which should equal
((FOSC x 0.85) / 4) /(bit rate) – 2
The nominal bit time for synchronization, which should equal (FOSC / 4) /(bit rate) – 2
Enables synchronization. Do not use this definition if using a crystal or resonator.
RX_ADVANCE
0x10
This is the receive advance. Use this definition to adjust center sampling for high bit
rates, 7400 bps or greater at 4 MHz. RX_ADVANCE must not be used in conjunction
with RX_DELAY.
RX_DELAY
0xF0
The receive delay. Use this definition to adjust center sampling for low bit rates, less
than 7400 bps at 4 MHz. For lower bit rates, the delay should be longer. Note, this
value is complimented (i.e., 0xF0 is a delay of 16 cycles). RX_DELAY must not be
used in conjunction with RX_ADVANCE.
IO_MASK_A
b'10111111'
Logical AND mask of the transmit pin.
IO_MASK_O
b'01000000'
Logical OR mask of the I/O pin.
RX_PIN
PORTC,7
The receive pin.
RX_PIN_DIR
TRISC,7
The receive pin direction control.
TX_PIN
PORTC,6
The transmit pin.
TX_PIN_DIR
TRISC,6
The transmit pin direction control.
TX_PORT
USE_GP_CHANGE
PORTC
N/A
 2002 Microchip Technology Inc.
The transmit pin port.
Use this definition to configure the external interrupt to be a GPIO interrupt on
change. The alternative is to use the INT pin.
DS00239A-page 5
AN239
USING THE DRIVER
The LIN Driver
After setting up a project with the LIN driver’s necessary files, it is time to start using the driver. This section
presents pertinent information about using the driver.
The important information addressed is:
The LIN slave driver is a state machine written for foreground processing. Being in the foreground implies the
function must be called often enough to retrieve data
from the receive buffer within the serial engine. Typically, the best place to call the driver is in the main program loop, and it should be called as often as possible.
Thus, if some application level tasks are sufficiently
long, then the driver function will most likely need to be
called more than once in the main loop.
•
•
•
•
•
•
Using the l_rxtx_driver function
Handling error flags
Handling finish flags
State flags within the driver
LIN ID events
Bus wake-up
The source code provided is a simple example on
using the LIN driver in an application.
FIGURE 4:
Figure 4 shows an example of what the main program
loop could look like with the call to the
l_txrx_driver function.
MAIN PROGRAM LOOP WITH CALL TO l_txrx_driver
Main
;Main application loop
call
l_txrx_driver
call
l_id_02_function
;Check for ID02 (tx)
btfsc
call
LF_RX
l_id_00_function
;Check for ID00 (rx)
movf
btfsc
goto
LIN_STATUS_FLAGS, W;Handle errors
STATUS, Z
Main
btfsc
goto
LE_BTO
PutLINToSleep
;Was the bus time exceeded?
clrf
goto
LIN_STATUS_FLAGS
Main
;Reset any errors
Finish Flags
There are two flags that indicate when the driver has
successfully transmitted or received data. The receive
flag is set when data has been received without error.
This flag must be cleared by the user after it is handled.
Likewise, the transmit flag indicates when data has
been successfully transmitted without error. The transmit flag must also be cleared by the user when it is handled. Figure 4 shows an example of checking the flags;
the flags are cleared in the calling function (not shown).
Error Flags
Certain error flags are set when expected conditions
are not met. For example, if the slave failed to generate
bit timing within the defined range, a sync error flag
(LE_SYNC) is set in the driver.
Errors are considered fatal until they are handled and
cleared. Thus, if the error is never cleared, then the
driver will ignore incoming data. Figure 4 shows an
example.
DS00239A-page 6
Notice that the errors are all contained within a single
register. Therefore, the LIN_STATUS_FLAGS register
can be checked for zero to determine if any errors did
occur.
Driver State Flags
The LIN driver uses state flags to remember where it is
between received bytes. After a byte is received, the
driver uses these flags to decide what is the next unexecuted state, then jumps to that state. One very useful
flag is the LS_BUSY flag. This bit indicates when the
driver is active on the bus; thus, this flag could be used
in applications that synchronize to the communications
on the bus. The other flags indicate what has been
received and what state the bus is in. Refer to
Appendix A for descriptions of the state flags. For most
situations, these flags will not need to be used within
the application.
 2002 Microchip Technology Inc.
AN239
ID Events and Functions
GENERAL INFORMATION
For each ID, there is an event function. The event function is required to tell the driver how to respond to the
data following the ID. For example, does the driver
need to prepare to receive or transmit data? Also, how
much data is expected to be received or transmitted?
Additional Interrupts
For successful operation three variables must be initialized, a pointer to data memory, frame time, and the
count, as shown in Figure 5.
FIGURE 5:
l_id_00
GLOBAL
movlw
movwf
movlw
addwf
movlw
movwf
retlw
VARIABLE INITIALIZATION
l_id_00
ID00_BUFF ;Set the pointer
LIN_POINTER
0x20
;Adjust the frame time
FRAME_TIME, F
0x02
;Set up the data count
LIN_COUNT
0x00
;Read
The pointer to memory tells the driver where to store
data for receiving or where to retrieve data for sending.
The frame time is the adjusted time, based on the
number of bytes to expect. Typically, the frame time
register will already have time left over from the header,
so time should be added to the register. For two bytes,
this would be an additional (30 + 1) * 1.4 bit times, or
43; the value 30 is the total bits of data, START bits, and
STOP bits, plus the checksum bits. The counter simply
tells the driver how much data to operate on. Note that
the count must always be initialized to something
greater than zero for the driver to function properly.
Waking the Bus
A LIN bus wake-up function, l_tx_wakeup, is provided for applications that need the ability to wake the
bus up. Calling this function will broadcast the wake-up
request character.
It is possible to add extra interrupts; however, it is not
recommended. The driver uses an external interrupt to
synchronize timing to the START edge. If additional
interrupts are added, then uncertainty is added to the
received START edge. Uncertainty in receiving the
START edge can severely degrade the maximum bit
rate under certain conditions.
There is a finite amount of uncertainty that is acceptable for a given bit rate and clock frequency, defined as
follows:
4N INS
1
----- – ( T E1 ( low ) + T E2 ( high ) + 2T ES ) = T w = --------------FOSC
BI
Without going into too much detail here, the above
equation basically derives the maximum number of
instructions related to uncertainty in terms of the ideal
bit rate and frequency (discussed later in this document). The real question is what instructions can be
counted in this uncertainty and the answer is, it
depends on the way the code is written for the application. It is also important to note that some uncertainty is
already assumed.
To be safe (i.e., not sacrifice reliability), avoid adding
any extra code to the interrupt unless your instruction
rate to bit rate ratio is greater than 200, or the number
of instructions added is extremely small.
With PIC18 devices, you have the option of using the
low priority interrupt vector for additional interrupts. The
high priority interrupt should be used for the LIN driver,
since it has precedence. The low priority interrupt could
be used for any other interrupt source not related to
LIN.
Definitions Using Prescalars
The prescaler definitions are set to achieve bit rates
between 4800 bps and 14400 bps, using a 4 MHz
clock source. It is possible to adjust these to achieve
lower bit rates or higher clock speeds. For example,
multiplying all the prescaler values by two would yield
much lower bit rates, if desired.
The LIN Event Handler
Event handling should be as short as possible. If the
event handler is long, unacceptable interbyte space
may be seen between receiving the ID byte and transmitting data from the slave to the master. Therefore,
choose the best method for decoding in your application. If you are only responding to a couple of IDs, then
simple XOR logical compares will suffice. If any more
IDs are responded to, then use a jump table. A complete jump table uses a significant amount of program
memory; however, it is very quick to decode IDs.
 2002 Microchip Technology Inc.
DS00239A-page 7
AN239
Calling the Driver
The Serial Engine
The driver is not a true background task, only the serial
communication is. Thus, the driver function must be
called frequently. There are two potential problems if
the driver function is not called frequently enough. The
receive buffer could be overrun, thus, the entire packet
would be corrupted. Another problem is unacceptable
interbyte space during slave to master transmissions.
To be safe, ensure the driver function is called at least
four times for every byte. The driver function will
execute very quickly if there is no action required.
The serial engine is interrupt driven firmware. It handles all bit level communication and synchronization.
The function requires an external interrupt source configurable to either an interrupt-on-change pin, or the
INT pin. Also, Timer0 is used to control asynchronous
communication.
With the access to the hardware stack on the PIC18
devices, it is possible to make the driver look like it is
operating in the background. Essentially, the address
of the driver function could be pushed onto the stack
upon interrupt. When the serial communications finishes, the address of the driver is pulled off the stack for
execution. when driver tasks are finished, control
returns to the application. This method is a possibility;
however, it is not shown.
Advance or Delay
After detecting a START edge for a serial byte, there is
a finite duration required to set up for the reception of
the byte. Depending on the bit rate and frequency, the
duration could put the sample point before or after the
center of the next received bit. Thus, the advance and
delay options are available. The delay is used to hold
sampling when the setup duration is shorter than half
the bit time. The advance is used to advance the bit
time for the next bit when the setup duration is longer
than half the bit time. The setup duration also includes
the time required to enter the interrupt, thus, the duration depends significantly on how the interrupt is setup.
PIC18 MCUs will have a slightly shorter setup time than
PIC16 MCUs, since time can be saved by using the fast
register stack.
IMPLEMENTATION
There are five functions found in the associated example firmware that control the operation of the LIN
interface:
•
•
•
•
•
LIN Transmit/Receive Driver
LIN Serial Engine
LIN Timekeeper
LIN Hardware Initialization
LIN Wake-up
DS00239A-page 8
SYNCHRONIZATION
Synchronization is performed by stretching the bit rate
clock and using the external interrupt to count the
edges of the sync byte. After the last falling edge of the
sync byte, the time is captured and compared to the
maximum and minimum bit time tolerances specified. If
within the tolerance, the value is used as the new
time-base.
TRANSMITTING WITH READBACK
The software UART handles asynchronous communications much like a hardware UART; it receives data
and generates errors under various conditions.
Because the LIN physical layer has a feedback path for
data (see Figure 6), the UART also reads back
transmitted data.
FIGURE 6:
SIMPLIFIED LIN
TRANSCEIVER
VBAT
Buffer
RX
PIC16
LIN bus
TX
Open Drain
The UART is designed to pre-sample before transmitting to capture feedback information. Transmit operations take 11 bit times to accurately capture the last bit
in the transmission.
SERIAL STATUS FLAGS
There are a few flags within the software UART to control its operation and to feed status information to functions outside the UART. The serial status flags are
listed and defined in Appendix A.
 2002 Microchip Technology Inc.
AN239
Transmit/Receive Driver
LIN Timers
The l_rxtx_driver is a state machine. Bit flags are
used to retain information about various states within
the driver. In addition, status flags are maintained to
indicate errors during transmit or receive operations.
The LIN specification identifies maximum frame times
and bus IDLE times. For this reason, a timekeeping
function is implemented. The timekeeping function
works together with the transmit/receive driver and the
transmit and receive functions. Essentially, the driver
and the transmit and receive functions update the
appropriate time, and bus and frame time when called.
If time-out conditions do occur, then status flags are set
to indicate the condition.
STATES AND STATE FLAGS
The LIN driver uses state flags to remember where it is
between received bytes. After a byte is received, the
driver uses these flags to decide what is the next unexecuted state, then jumps to that state. Figure 7 and
Figure 8 outline the program flow through the different
states. The states and state flags are listed and defined
in Appendix A.
TX/RX TABLE
A transmit/receive table is provided to determine how
to handle data after the node has successfully received
the ID byte. The table returns information to the
transmit/receive driver about data size and direction.
STATUS FLAGS
Within various states, status flags may be set depending on certain conditions. For example, if the slave
receives a corrupted checksum, then a checksum error
is indicated through a status flag. Unlike state flags,
status flags are not reset automatically. Status flags are
left for the LIN system designer to act upon within the
higher levels of the firmware. The status flags are listed
and defined in Appendix A.
 2002 Microchip Technology Inc.
Hardware Initialization
An initialization function, l_init, is provided to setup
the necessary hardware settings. Also, the state and
status flags are all cleared. This function can also be
used to reset the LIN driver.
Wake-up
The only time the slave can transmit to the bus without
a request is when the bus is sleeping. Basically, any
slave can transmit a wake-up signal. For this reason, a
wake-up function is defined, and it sends a wake-up
signal when called.
DS00239A-page 9
AN239
FIGURE 7:
RECEIVE HEADER PROGRAM FLOW
A
Requesting
Wake-up?
Yes
Read Back Test,
Set Flags
No
Test Break, Set
Flags
No
Update Bus Timer
Got Break?
Yes
Build Option
Got Sync?
No
Measure and
Test, Set Flags
No
Test ID, Determine
RX or TX,
Determine Data
Count, Set Frame
Timer, Set Flags
Yes
Got ID?
Yes
TX
B
DS00239A-page 10
TX or RX?
RX
Finish
 2002 Microchip Technology Inc.
AN239
FIGURE 8:
TRANSMIT/RECEIVE MESSAGE PROGRAM FLOW
B
TX or RX?
Test, Set Flags
No
RX
TX
Got Whole
Message?
Read Back?
No
Test, Set Flags
No
Test, Set Flags
No
Test, Set Flags
Yes
Yes
Sent Whole
Message?
Read Checksum
Yes
Sent Checksum?
Yes
Reset State Flags
Finish
 2002 Microchip Technology Inc.
DS00239A-page 11
AN239
FIGURE 9:
TIMEKEEPING PROGRAM FLOW
Start
LIN bus Sleeping?
Yes
No
Update Bus Time
Test for Time-out
No
Active TX/RX?
Yes
Update Frame
Time, Test for
Time-out
Finish
EVALUATING OPERATING REGION
SAMPLING
It is important to understand the relationship between
bit rate and clock frequency when designing a slave
node in a LIN network. Therefore, this section focuses
on developing this understanding based on the LIN
specification. It is assumed that the physical limits
defined in the LIN specification are reasonable and
accurate. This section merely uses the defined physical
limits and does not present any analysis of the limits
defined for physical interface to the LIN bus. Essentially, the focus of this section is to analyze the firmware
and its performance based on the defined conditions in
the LIN specification.
The ideal sampling point is assumed to be the center of
the incoming bit, as shown in Figure 10. The equations
presented in the following sections use this point as the
reference.
General Information
Some general information used throughout the
analysis is provided here.
DATA RATE VS. SAMPLING RATE
There are essentially two rates to compare: the incoming data rate and the sampling rate. The slave node
only has control of the sampling rate; therefore, for this
discussion, the logical choice for a reference is the
incoming data rate, BI. The equations that follow
assume BI is the ideal data rate of the system.
FIGURE 10:
SAMPLING
RELATING CLOCK FREQUENCY ERROR TO
BIT ERROR
The LIN specification refers to clock frequency error
rather than bit error. Because of this, the LIN system
designer must design the system with like clock sources;
however, this is rather impractical. It is more feasible to
have clock sources designed for the individual needs of
the node. All of the equations in this section refer to bit
error, rather than frequency error. The following equation
relates frequency error to bit rate error:
1
---------------- – 1 = EB
1 + EF
For very low clock frequency errors, the bit rate error
can be approximated by: – E F ≈ E B
Thus, a ±2% frequency error is nearly the same bit rate
error.
DS00239A-page 12
 2002 Microchip Technology Inc.
AN239
Acceptable Bit Rate Error
The LIN specification allows for a ±2% error for master/slave communications. This section evaluates this
tolerance based on specified worst case conditions
(slew rate, voltage, and threshold) and the
implementation.
FIGURE 13:
IDEAL SAMPLING WINDOW
It is relatively easy to see the maximum allowed error
in the ideal situation. Ideal is meant by infinite slew rate
with a purely symmetrical signal, like the signal shown
in Figure 11.
FIGURE 11:
The LIN specification defines a tolerable slew rate
range and threshold. The worst case is the minimum
slew rate at the maximum voltage, 1V/µs and 18V,
according to the LIN specification. The threshold is
above 60% and below 40% for valid data. Figure 13
shows the basic measurements.
ADJUSTED BIT TIME ERROR
VBAT
60%
40%
IDEAL WINDOW
VBAT
TEI
TES
Taking the difference of the ideal maximum time and
the slight adjustment due to specified operating
conditions yields the following error time adjustment:
TE
Basically, if the data sampling is greater or less than
half of one bit time, TE, over nine bits, the last bit in the
transmission will be interpreted incorrectly. Figure 12
graphically depicts how data may be misinterpreted
because of misaligned data and sampling rates.
FIGURE 12:
DATA VS SAMPLING
Ideal
Slow
Fast
The following two equations give the maximum and
minimum bit rates based on shifting time by one-half of
one bit time or TE = ±1/(2BI).
1 TE
1
----- – ------ = -----------BI 9
Bmax
1 TE
1
----- + ------ = ----------BI 9
Bmin
SHORTENED WINDOW DUE TO SLEW RATE
1
( 0.5V – 0.4V )
T EI – T ES = -------- – --------------------------------- = T E
2B I ( dV ) ⁄ ( dt ) min
Therefore, TE is slightly smaller than the ideal case,
and the minimum and maximum equations in the
previous section yield a slightly narrower range for bit
rate.
OFFSETS
An offset is a less than ideal sample point. For example, it is possible for a software UART to take a sample
before or after the center point of an incoming bit, as
shown in Figure 14. This is related to an offset from the
START edge and ultimately shifts the bit rate error to
favor one side over the other. For example, if the
START edge detection is delayed for 10 µs from the
center of a 9.6 Kbit transmission, the absolute range for
bit rate error is -4.1% and +6.9%.
FIGURE 14:
OFFSET FROM CENTER
VBAT
60%
40%
TEE
TO
TEI
Although the ideal sampling window may be a useful
approximation at very low bit rates, slew rate and
threshold must be accounted for at higher rates. The
ideal analysis serves as a base for more realistic
analysis.
 2002 Microchip Technology Inc.
DS00239A-page 13
AN239
The example firmware leaves the Timer0 interrupt
enabled at all times to maintain some basic time about
the LIN bus activity. A side effect of this is unpredictable
offset. For example, if a START edge occurs while program execution is in an interrupt, the interrupt routine
must finish before the START edge can be Acknowledged. Therefore, an undetermined offset from the
START edge occurs.
Although the exact offset cannot be determined when
interrupts are enabled, it is possible to determine a
maximum offset. Basically, the maximum offset is
related to the longest time through the interrupt when
looking for a START edge. Having the maximum offset
leads to the maximum bit rate.
The same equations apply as before; however, TE is
different for the maximum and minimum bit rate,
because there is no time symmetry.
1 T E1
1
----- – --------- = -----------BI
9
B max
1 T E2
1
----- + --------- = ----------9
BI
Bmin
TE1 and TE2 are related:
1
----- – 2T ES = T E1 + T E2
BI
where:
FIGURE 15:
ABSOLUTE OFFSET WINDOW
VBAT
60%
40%
TE1(low)
Tw
TE2(high)
The 4/FOSC term is the instruction time. Multiplying the
instruction time by the number of executed instructions
in the interrupt routine results in the total time through
the interrupt.
Substituting the time equations TE1(low), TE2(high), and
TES, and solving BI yields the maximum bit rate:
0.6399
BI = --------------------------4N
------- – 1.8µs
F
Adjusting this down by 15% to allow for synchronization
tolerances leads to maximum allowable bit rate. For
example, for a slave node operating at 4 MHz with a
maximum instruction count of 40 through an interrupt,
the maximum ideal bit rate would be about 14.2 kbps.
Beyond 14.2 kbps, there is a significant probability that
incoming data will be misinterpreted.
T E2 = T EI – T ES – T O
Minimum Samples Per Bit
T E1 = T EI – T ES + T O
Given a finite bit rate error range and finite control of the
bit rate, leads to areas where the slave cannot operate.
These are basically gaps where the error is outside the
defined bit rate error range for a particular number of
instructions per bit. This section provides the mathematical basis for these gaps. The equations developed
in this section are provided to help the LIN designer
build a robust network.
Ultimately, the LIN specification requires that the slave
accept as much as a ±2% error between the incoming
bit rate (BI) and the sampling bit rate. TE1 and TE2 have
specific limits for offsets before and after the center
sampling point. They are:
– 9 ( – 0.02 )
T E2 ( high ) = -------------------------( 0.98 ) ( B I )
9 ( 0.02 )
T E1 ( low ) = -------------------------( 1.02 ) ( BI )
With these times, the total window time shown in
Figure 15, can be calculated to determine the
maximum allowable offset or the maximum interrupt
duration:
4N INS
1
----- – ( T E1 ( low ) + T E2 ( high ) + 2T ES ) = T w = --------------FOSC
BI
DS00239A-page 14
FREQUENCY RANGE
The following equation determines the clock frequency
as a function of the number of instructions executed per
bit, bit rate, and bit rate error.
FOSC = ( EB + 1 ) ( N ) ( 4 ) ( B )
 2002 Microchip Technology Inc.
AN239
OVERLAPPING OPERATION
For a large number of instructions executed per bit, the
slave will synchronize and communicate well with the
master. However, for a particular error range, ±2%, with
higher bit rates and lower clock frequencies, the slave
may never synchronize and communicate.
To approach this problem, the minimum frequency for
a number of instructions (EL+1)(N)(4)(BI) must be compared to the maximum frequency for one less number
of instructions (EH+1)(N-1)(4)(BI). Where these are
equal is the border between continuous and
discontinuous operation for any given input frequency:
( EL + 1 ) ( N ) ( 4 ) ( B I ) = ( EH + 1 ) ( N – 1 ) ( 4 ) ( B I )
Solving this equation yields:
( EH + 1 )
N low = -----------------------------------------------( EH + 1 ) – ( EL + 1 )
Therefore, the minimum number of instructions, Nlow,
must be executed per bit to accept the defined error.
For example, for a ±2% error, the lowest number of
instructions accepted before certain clock frequency/bit
rate combinations become a problem is 26. Note that
the value of 26 is much lower than the number of
instructions through the interrupt.
 2002 Microchip Technology Inc.
POSSIBLE ALTERNATE
IMPLEMENTATION
The bit banged firmware code referenced in this application note utilizes the Timer0 module and an external
interrupt. It is also possible to use the CCP and Timer1
module to perform the same function. The results are
nearly the same as the implementation presented here.
MEMORY USAGE
The firmware code size depends on the build conditions. As it is currently built with the example application, the firmware occupies 412 words of program
memory and 46 bytes of data memory.
REFERENCES
LIN Specification Package Revision 1.2,
http://www.lin-subbus.org/
MPASM™ User’s Guide with MPLINK™ and MPLIB™,
Microchip Technology Incorporated, 1999
DS00239A-page 15
AN239
APPENDIX A:
TABLE A-1:
SYMBOLS
FUNCTIONS
Function Name
Purpose
l_init
Call this function to initialize or reset the hardware associated to the LIN interface.
l_tx_wakeup
Wake-up function. Call this function to wake-up the bus if asleep.
l_txrx_driver
The core transmit and receive function, which manages transmit and receive operations to the bus.
State flags are set and cleared within this function. Status flags are also set based on certain
conditions (i.e., errors).
l_txrx_table
This function is called by the transmit/receive daemon after the identifier byte has been received.
Message length and direction is returned to the driver. Within the table, pointers could be set up for
different identifiers.
SerialEngine
This is the interrupt driven software UART.
UpdateTimer
Used to update the bus and frame timers.
TABLE A-2:
REGISTERS
Variable Name
Purpose
BUS_TIME
Bus timer.
FRAME_TIME
8-bit frame timer register.
HEADER_TIME
Same as FRAME_TIME.
LIN_CHKSUM
Used by the driver to calculate checksum for transmit and receive.
LIN_COUNT
Used by the driver to maintain a message data count.
LIN_FINISH_FLAGS
Contains flags indicating completion of transmit and receive data.
LIN_ID
Holding register for the received identifier byte. This register is used in the l_txrx_table function to
determine how the node should react.
LIN_POINTER
Pointer to a storage area used by the driver. Data is either loaded into or read from memory depending
on the identifier.
LIN_READBACK
Holding register for transmitted data to be compared with received data for bit error detection.
LIN_STATE_FLAGS
Flags to indicate what state the LIN bus is in.
LIN_STATE_FLAGS2
Additional flags to indicate what state the LIN bus is in.
LIN_STATUS_FLAGS
Contains status information about the LIN bus.
RXDATA
The Least Significant Byte of the receive shift register. The data is also pulled from this register after a
complete receive.
RXSR_2
The Most Significant Byte of the receive shift register.
RXTX_COUNT
Bit counter register for the software UART.
SERIAL_FLAGS
This register holds the flags to control the software UART.
TIME_BASE
This register holds the time per bit based on the number of instructions.
TXSR
The Most Significant Byte of the transmit shift register.
TXSR_2
The Least Significant Byte of the transmit shift register.
DS00239A-page 16
 2002 Microchip Technology Inc.
AN239
TABLE A-3:
Flag Name
FLAGS
Register
Meaning
LE_BIT
LIN_STATUS_FLAGS
Indicates a bit error.
LE_BRK
LIN_STATUS_FLAGS
Indicates a failure to receive a valid break.
LE_BTO
LIN_STATUS_FLAGS
Indicates a bus activity time-out error.
LE_CHKSM
LIN_STATUS_FLAGS
Indicates a checksum error during a receive.
LE_FTO
LIN_STATUS_FLAGS
Indicates a frame time-out error.
LE_GEN
LIN_STATUS_FLAGS
Indicates a general error, typically a framing error.
LE_PAR
LIN_STATUS_FLAGS
Indicates a parity error.
LE_SYNC
LIN_STATUS_FLAGS
Indicates a synchronization tolerance error.
LF_RX
LIN_FINISH_FLAGS
Indicates data has been received.
LF_TX
LIN_FINISH_FLAGS
Indicates data has been sent.
LS_BRK
LIN_STATE_FLAGS
Indicates a break has been received.
LS_BUSY
LIN_STATE_FLAGS
Indicates the LIN bus is busy.
LS_CHKSM
LIN_STATE_FLAGS
Indicates the checksum has been sent or received.
LS_DATA
LIN_STATE_FLAGS
Indicates all data has been sent or received.
LS_ID
LIN_STATE_FLAGS
Indicates the identifier has been received.
LS_RBACK
LIN_STATE_FLAGS
Indicates a read back is pending.
LS_SLPNG
LIN_STATE_FLAGS
Indicates the LIN bus is sleeping.
LS_SYNC
LIN_STATE_FLAGS
Indicates a sync byte has been received.
LS_TXRX
LIN_STATE_FLAGS
Indicates transmit or receive operation.
LS_WAKE
LIN_STATE_FLAGS
Indicates a wake-up has been requested (this node only).
S_BUSY
SERIAL_FLAGS
Indicates whether the serial engine is busy or not.
S_FERR
SERIAL_FLAGS
Indicates an invalid STOP bit was received.
S_RXIF
SERIAL_FLAGS
Indicates data has been received.
S_SSRT
SERIAL_FLAGS
Indicates the serial engine is waiting for a start of sync.
S_SYNC
SERIAL_FLAGS
Indicates the serial engine is syncing.
S_SYNCERR
SERIAL_FLAGS
Indicates a failure to sync.
S_TXRX
SERIAL_FLAGS
Indicates the UART is transmitting or receiving.
 2002 Microchip Technology Inc.
DS00239A-page 17
AN239
TABLE A-4:
COMPILE TIME DEFINITIONS
Definition Name
Value
Description
d'11'
Sets the receive break threshold. For low tolerance oscillator sources, this value
should be ‘11’, for high tolerance sources this value should be ‘9’.
LIN_ACTVE_TIME_PS
b'10001000'
The value loaded into the option register when the slave is actively receiving or
transmitting on the LIN bus. A prescale value of 1x is ideal for bit rates between
4800 bps and 14400 bps at 4 MHz.
LIN_IDLE_TIME_PS
b'10010110'
The value loaded into the option register when the LIN bus is IDLE. A prescale
setting of 128x is the desired choice for the prescaler.
LIN_SYNC_TIME_PS
b'10010010'
The value loaded into the option register when the slave is capturing the sync byte. A
prescale setting of 8x is the desired choice for the prescaler.
BRK_THRESHOLD
MAX_BIT_TIME
MAX_HEADER_TIME
d'118'
d'39'
The upper boundary bit time for synchronization, which should equal
((FOSC x 1.15) / 4) /(bit rate) – 2
The maximum allowable time for the header. This value equals ((34 + 1) x 1.4) – 10,
and should not be changed unless debugging.
MAX_IDLE_TIME
d'195'
Defines the maximum bus IDLE time; the spec defines this to be 25000 bit times.
The value equals 25000 / 128. The 128 comes from the LIN_IDLE_TIME_PS
definition.
MAX_TIME_OUT
d'128'
Specifies the maximum time out between wake-up requests. The LIN specification
defines this to be 128 bit times.
MIN_BIT_TIME
d'87'
NOM_BIT_TIME
d'102'
RC_OSC
N/A
The lower boundary bit time for synchronization, which should equal
((FOSC x 0.85) / 4) /(bit rate) – 2
The nominal bit time for synchronization, which should equal (FOSC / 4) /(bit rate) – 2
Enables synchronization. Do not use this definition if using a crystal or resonator.
RX_ADVANCE
0x10
This is the receive advance. Use this definition to adjust center sampling for high bit
rates, 7400 bps or greater at 4 MHz. RX_ADVANCE must not be used in conjunction
with RX_DELAY.
RX_DELAY
0xF0
The receive delay. Use this definition to adjust center sampling for low bit rates, less
than 7400 bps at 4 MHz. For lower bit rates, the delay should be longer. Note, this
value is complimented (i.e., 0xF0 is a delay of 16 cycles). RX_DELAY must not be
used in conjunction with RX_ADVANCE.
IO_MASK_A
b'10111111'
Logical AND mask of the transmit pin.
IO_MASK_O
b'01000000'
Logical OR mask of the I/O pin.
RX_PIN
PORTC,7
The receive pin.
RX_PIN_DIR
TRISC,7
The receive pin direction control.
TX_PIN
PORTC,6
The transmit pin.
TX_PIN_DIR
TRISC,6
The transmit pin direction control.
TX_PORT
USE_GP_CHANGE
DS00239A-page 18
PORTC
N/A
The transmit pin port.
Use this definition to configure the external interrupt to be a GPIO
interrupt-on-change. The alternative is to use the INT pin.
 2002 Microchip Technology Inc.
AN239
APPENDIX B:
SOURCE CODE
Due to size considerations, the complete source code
for this application note is not included in the text. A
complete version of the source code, with all required
support files, is available for download as a Zip archive
from the Microchip web site, at:
www.microchip.com
 2002 Microchip Technology Inc.
DS00239A-page 19
AN239
NOTES:
DS00239A-page 20
 2002 Microchip Technology Inc.
Note the following details of the code protection feature on Microchip devices:
•
Microchip products meet the specification contained in their particular Microchip Data Sheet.
•
Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
•
There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip's Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
•
Microchip is willing to work with the customer who is concerned about the integrity of their code.
•
Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products.
Information contained in this publication regarding device
applications and the like is intended through suggestion only
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
No representation or warranty is given and no liability is
assumed by Microchip Technology Incorporated with respect
to the accuracy or use of such information, or infringement of
patents or other intellectual property rights arising from such
use or otherwise. Use of Microchip’s products as critical components in life support systems is not authorized except with
express written approval by Microchip. No licenses are conveyed, implicitly or otherwise, under any intellectual property
rights.
Trademarks
The Microchip name and logo, the Microchip logo, KEELOQ,
MPLAB, PIC, PICmicro, PICSTART and PRO MATE are
registered trademarks of Microchip Technology Incorporated
in the U.S.A. and other countries.
FilterLab, microID, MXDEV, MXLAB, PICMASTER, SEEVAL
and The Embedded Control Solutions Company are
registered trademarks of Microchip Technology Incorporated
in the U.S.A.
dsPIC, dsPICDEM.net, ECONOMONITOR, FanSense,
FlexROM, fuzzyLAB, In-Circuit Serial Programming, ICSP,
ICEPIC, microPort, Migratable Memory, MPASM, MPLIB,
MPLINK, MPSIM, PICC, PICDEM, PICDEM.net, rfPIC, Select
Mode and Total Endurance are trademarks of Microchip
Technology Incorporated in the U.S.A. and other countries.
Serialized Quick Turn Programming (SQTP) is a service mark
of Microchip Technology Incorporated in the U.S.A.
All other trademarks mentioned herein are property of their
respective companies.
© 2002, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
Microchip received QS-9000 quality system
certification for its worldwide headquarters,
design and wafer fabrication facilities in
Chandler and Tempe, Arizona in July 1999
and Mountain View, California in March 2002.
The Company’s quality system processes and
procedures are QS-9000 compliant for its
PICmicro® 8-bit MCUs, KEELOQ® code hopping
devices, Serial EEPROMs, microperipherals,
non-volatile memory and analog products. In
addition, Microchip’s quality system for the
design and manufacture of development
systems is ISO 9001 certified.
 2002 Microchip Technology Inc.
DS00239A - page 21
WORLDWIDE SALES AND SERVICE
AMERICAS
ASIA/PACIFIC
Corporate Office
Australia
2355 West Chandler Blvd.
Chandler, AZ 85224-6199
Tel: 480-792-7200 Fax: 480-792-7277
Technical Support: 480-792-7627
Web Address: http://www.microchip.com
Microchip Technology Australia Pty Ltd
Suite 22, 41 Rawson Street
Epping 2121, NSW
Australia
Tel: 61-2-9868-6733 Fax: 61-2-9868-6755
Rocky Mountain
China - Beijing
2355 West Chandler Blvd.
Chandler, AZ 85224-6199
Tel: 480-792-7966 Fax: 480-792-4338
Atlanta
500 Sugar Mill Road, Suite 200B
Atlanta, GA 30350
Tel: 770-640-0034 Fax: 770-640-0307
Boston
2 Lan Drive, Suite 120
Westford, MA 01886
Tel: 978-692-3848 Fax: 978-692-3821
Chicago
333 Pierce Road, Suite 180
Itasca, IL 60143
Tel: 630-285-0071 Fax: 630-285-0075
Dallas
4570 Westgrove Drive, Suite 160
Addison, TX 75001
Tel: 972-818-7423 Fax: 972-818-2924
Detroit
Tri-Atria Office Building
32255 Northwestern Highway, Suite 190
Farmington Hills, MI 48334
Tel: 248-538-2250 Fax: 248-538-2260
Kokomo
2767 S. Albright Road
Kokomo, Indiana 46902
Tel: 765-864-8360 Fax: 765-864-8387
Los Angeles
18201 Von Karman, Suite 1090
Irvine, CA 92612
Tel: 949-263-1888 Fax: 949-263-1338
San Jose
Microchip Technology Inc.
2107 North First Street, Suite 590
San Jose, CA 95131
Tel: 408-436-7950 Fax: 408-436-7955
Toronto
6285 Northam Drive, Suite 108
Mississauga, Ontario L4V 1X5, Canada
Tel: 905-673-0699 Fax: 905-673-6509
Microchip Technology Consulting (Shanghai)
Co., Ltd., Beijing Liaison Office
Unit 915
Bei Hai Wan Tai Bldg.
No. 6 Chaoyangmen Beidajie
Beijing, 100027, No. China
Tel: 86-10-85282100 Fax: 86-10-85282104
China - Chengdu
Microchip Technology Consulting (Shanghai)
Co., Ltd., Chengdu Liaison Office
Rm. 2401, 24th Floor,
Ming Xing Financial Tower
No. 88 TIDU Street
Chengdu 610016, China
Tel: 86-28-86766200 Fax: 86-28-86766599
China - Fuzhou
Microchip Technology Consulting (Shanghai)
Co., Ltd., Fuzhou Liaison Office
Unit 28F, World Trade Plaza
No. 71 Wusi Road
Fuzhou 350001, China
Tel: 86-591-7503506 Fax: 86-591-7503521
China - Shanghai
Microchip Technology Consulting (Shanghai)
Co., Ltd.
Room 701, Bldg. B
Far East International Plaza
No. 317 Xian Xia Road
Shanghai, 200051
Tel: 86-21-6275-5700 Fax: 86-21-6275-5060
China - Shenzhen
Microchip Technology Consulting (Shanghai)
Co., Ltd., Shenzhen Liaison Office
Rm. 1315, 13/F, Shenzhen Kerry Centre,
Renminnan Lu
Shenzhen 518001, China
Tel: 86-755-82350361 Fax: 86-755-82366086
China - Hong Kong SAR
Microchip Technology Hongkong Ltd.
Unit 901-6, Tower 2, Metroplaza
223 Hing Fong Road
Kwai Fong, N.T., Hong Kong
Tel: 852-2401-1200 Fax: 852-2401-3431
India
Microchip Technology Inc.
India Liaison Office
Divyasree Chambers
1 Floor, Wing A (A3/A4)
No. 11, O’Shaugnessey Road
Bangalore, 560 025, India
Tel: 91-80-2290061 Fax: 91-80-2290062
Japan
Microchip Technology Japan K.K.
Benex S-1 6F
3-18-20, Shinyokohama
Kohoku-Ku, Yokohama-shi
Kanagawa, 222-0033, Japan
Tel: 81-45-471- 6166 Fax: 81-45-471-6122
Korea
Microchip Technology Korea
168-1, Youngbo Bldg. 3 Floor
Samsung-Dong, Kangnam-Ku
Seoul, Korea 135-882
Tel: 82-2-554-7200 Fax: 82-2-558-5934
Singapore
Microchip Technology Singapore Pte Ltd.
200 Middle Road
#07-02 Prime Centre
Singapore, 188980
Tel: 65-6334-8870 Fax: 65-6334-8850
Taiwan
Microchip Technology (Barbados) Inc.,
Taiwan Branch
11F-3, No. 207
Tung Hua North Road
Taipei, 105, Taiwan
Tel: 886-2-2717-7175 Fax: 886-2-2545-0139
EUROPE
Austria
Microchip Technology Austria GmbH
Durisolstrasse 2
A-4600 Wels
Austria
Tel: 43-7242-2244-399
Fax: 43-7242-2244-393
Denmark
Microchip Technology Nordic ApS
Regus Business Centre
Lautrup hoj 1-3
Ballerup DK-2750 Denmark
Tel: 45 4420 9895 Fax: 45 4420 9910
France
Microchip Technology SARL
Parc d’Activite du Moulin de Massy
43 Rue du Saule Trapu
Batiment A - ler Etage
91300 Massy, France
Tel: 33-1-69-53-63-20 Fax: 33-1-69-30-90-79
Germany
Microchip Technology GmbH
Steinheilstrasse 10
D-85737 Ismaning, Germany
Tel: 49-89-627-144 0 Fax: 49-89-627-144-44
Italy
Microchip Technology SRL
Centro Direzionale Colleoni
Palazzo Taurus 1 V. Le Colleoni 1
20041 Agrate Brianza
Milan, Italy
Tel: 39-039-65791-1 Fax: 39-039-6899883
United Kingdom
Microchip Ltd.
505 Eskdale Road
Winnersh Triangle
Wokingham
Berkshire, England RG41 5TU
Tel: 44 118 921 5869 Fax: 44-118 921-5820
10/18/02
DS00239A-page 22
 2002 Microchip Technology Inc.
Similar pages