MICROCHIP HCS360 Technical data

HCS360

KEELOQ® Code Hopping Encoder

FEATURES

Security

• Programmable 28/32-bit serial number

• Programmable 64-bit encryption key

• Each transmission is unique

• 67-bit transmission code length

• 32-bit hopping code

• 35-bit fixed code (28/32-bit serial number,
4/0-bit function code, 1-bit status, 2-bit CRC)

• Encryption keys are read protected

Operating

• 2.0-6.6V operation

• Four but ton inputs

- 15 functions available

• Selectable baud rate

• Automatic code word co mpletion

• Battery low signal transmitted to receiver

• Nonvolatile synchronization data

• PWM and Manchester modulation

Other

• Easy-to-use programming interface

• On-chip EEPROM

• On-chip oscillator and timing components

• Button inputs have inte rnal pull-down resistors

• Current limiting on LED

• Minimum component count

Enhanced Features Over HCS300

• 48-bit seed vs. 32-bit seed

• 2-bit CRC for error detection

• 28/32-bit serial number select

• Two seed transmission methods

• PWM and Manchester modulation

• IR Modulation mode

output

DESCRIPTION

The HCS360 is a code hopping encoder designed for
secure Remote Keyless Entry (RKE) systems. The
HCS360 utilizes the KEELOQ c ode ho pping techno logy,
which incorporates high security, a small package
outline and low cost, to make this device a perfect
solution for unidirectional remote keyless entry sys­tems and access control systems.

PACKAGE TYPES

PDIP, SOIC

8

V

S0

S1
S2

S3

1

HCS360

2
3
4

DD

LED

7
6

DATA

V

SS

5

BLOCK DIAGRAM

LED

DATA

RESET circuit

VSS

VDD

Oscillator

Controller

LED driver

EEPROM

32-bit shift register

Button input port

Encoder

Power
latching
and
switching

Typical Applications

The HCS360 is ideal for Remote Keyless Entry (RKE)
applications. These applications include:

• Automotive RKE systems

• Automotive alarm systems

The HCS360 combines a 32-bit hopping code
generated by a nonlinear encryption algorithm, with a
28/32-bit serial number and 7/3 status bits to create a
67-bit transmission stream.

S

S

S1S

2

3

0

• Automotive immobilizers

• Gate and garage door openers

• Identity t okens

• Burglar alarm systems

 2002 Microchip Technology Inc. DS40152E-page 1

HCS360

The crypt key, serial number and conf iguration d ata are
stored in an EEPROM array which is n ot accessible via
any external connection. The EEPROM data is pro­grammable but read-protected. The data can be veri­fied only after an automatic erase and programming
operation. This protects against attempts to gain
access to keys or manipulate synchronizat ion values.
The HCS360 provides an easy-to-use serial interface
for programming the necessary keys, system parame­ters and configuration data.

1.0 SYSTEM OVERVIEW

Key Terms

The following is a l ist of key te rms us ed thro ughout this
data sheet. For additional information on K
Code Hopping, refer to Technical Brief 3 (TB003).

• RKE - Remote Keyless Entry

• Button Status - Indicates what button input(s)
activated the transmission. Encompasses the 4
button status bits S3, S2, S1 and S0 (Figure 3-1).

• Code Hopping - A method by which a code,
viewed externally to the system, appears to
change unpredictably each time it is transmitted.

• Code word - A block of data that is repeatedly
transmitted upon button activation (Figure3-1).

• Transmission - A data stream consisting of
repeating code words (Figure 8-1).

• Crypt key - A unique and secret 64-bit number
used to encrypt and decrypt data. In a symmetri­cal block cipher such as the K
the encryption and de cry pti on k ey s a re equal and
will therefore be referred to generally as the crypt
key.

• Encoder - A device that generates and encodes
data.

• Encryption Algorithm - A recipe wher eby data i s
scrambled using a cryp t key . The dat a can only be
interpreted by the respe ctive dec ryptio n algo rithm
using the same crypt key.

• Decoder - A device that decodes data received
from an encoder.

• Decryption algorithm - A recipe whereby data
scrambled by an encryption algorithm can be
unscrambled using the s ame crypt key.

EELOQ algorithm,

EELOQ and

• Learn – Learning involves the receive r calculatin g
the transmitter’s appropriate crypt ke y, d ec rypting
the received hopping code and storing the serial
number, synchronization counter value and crypt
key in EEPROM. The K

itates several learning strategies to be imple­mented on the decoder. The following are
examples of what can be done.

- Simple Learning

The receiver uses a fixed crypt key, common
to all compone nts of al l s y ste ms b y the same
manufacturer, to decrypt the received code

word’s encrypted portion.

- Normal Learning

The receiver uses information transmitted
during normal operation to derive the crypt
key and decrypt the received code word’s
encrypted portion.

- Secure Learn

The transmitter is activated through a special
button combinat ion to t ransmit a stored 60-bit
seed value used to generat e the trans mitter’s
crypt key. The receiver uses this seed value
to derive the same crypt key and decrypt the
received code word’s encrypted portion.

• Manufacturer’s code – A unique and secret 64-
bit number used to generate un ique encoder crypt
keys. Each encoder is programmed with a crypt
key that is a function of the manufacturer’s code.
Each decoder is programmed with the manufac­turer code itself.

The HCS360 code hopping encode r is designed sp ecif­ically for keyless entry systems; primarily vehicles and
home garage door openers. The encoder portion of a
keyless entry system is integrated into a transmitter,
carried by the user and operated to gain access to a
vehicle or restricted area. The HCS360 is meant to be
a cost-effective yet secure solution to such systems,
requiring very few external components (Figure 2-1).

Most low-end keyless entry transmitters are given a
fixed identificati on code that is transmitted ever y time a
button is pushed. The number of unique identification
codes in a low-end system is usually a relatively small
number. These shortcomings provide an opportunity

for a soph istic ated t hief to crea te a d evice that ‘grab s’
a transmission and retransmits it later, or a device that
quickly ‘scans ’ all pos sible identi ficati on c odes un til the
correct one is found.

The HCS360, on the other hand, employs the K
code hopping technology coupled with a transmission
length of 66 bits to virtually eliminate the use of code
‘grabbing’ or code ‘scann ing’. The hig h security le vel of
the HCS360 is ba sed on the p ate nted K
ogy. A block cipher based on a block length of 32 bits
and a key length of 64 bits is used. The algorithm
obscures the informati on i n such a way that even if th e
transmission informati on (before c oding) dif fers b y only
one bit from that of the previous transmission, the next

EELOQ product family facil-

EELOQ

EELOQ

technol-

DS40152E-page 2  2002 Microchip Technology Inc.

HCS360

coded transmission will be completely different. Statis­tically, if only one bit in the 32-bit string of information
changes, greater than 50 percent of the coded trans­mission bits will change.

As indicated in the block diagram on page one, the
HCS360 has a small EEPROM array which must be
loaded with several p arameters before use; mos t ofte n
programmed by the manufacturer at the time of produc­tion. The most important of these are:

• A 28-bit serial number, typically unique for every
encoder

• A crypt key

• An initial 16-bit synchronization value

• A 16-bit configuration value

The crypt key generatio n typically input s the transmitter
serial number and 64-bit manufact urer ’s code into t he
key generation algorithm (Figure 1-1). The manufac­turer’s code is chosen by the system manufacturer and
must be carefully controlled as it is a pivotal part of the
overall system security.

FIGURE 1-1: CREATION AND STORAGE OF CRYPT KEY DURING PRODUCTION

Production
Programmer

Manufacturer’s

Code

Transmitter

Serial Number

Key

Generation

Algorithm

Crypt

Key

HCS360

EEPROM Array

Serial Number

Crypt Key
Sync Counter

.

.

.

The 16-bit synchronization counter is the basis behind
the transmitted code word changing for each transmis­sion; it increments each time a button is pressed. Due
to the code hoppin g algorith m’s complex ity, each i ncre­ment of the synchronization value results in greater
than 50% of the bits changing in the transmitted code
word.

Figure 1-2 shows how the key values in EEPROM are
used in the encoder . O nce the encoder dete cts a button
press, it reads the button inputs and updates the syn­chronization counter. The synchronization counter and
crypt key are input to the encryption algorithm and the
output is 32 bits of encrypted information. This data will
change with every button press, its value appearing
externally to ‘ran domly h op aroun d’, hence it is re ferred
to as the hopping portion of the code word. The 32-bit
hopping code is combined with the button information
and serial numb er to fo rm the code word transm itted to
the receiver. The code word format is explained in
greater detail in Section 4.2.

A receiver may use any type of controller as a decoder,
but it is typically a microcontroller with compatible firm­ware that allows the decoder to operate in conjunction
with an HCS360 based transmitter. Section 7.0
provides detail on integrating the HCS360 into a sys­tem.

A transmitter must first be ‘learned’ by the receiver
before its use is allowed in the system. Learning
includes calculating the transmitter’s appropriate crypt
key, decrypting the received hopping code and storing
the serial number, synchronization counter value and
crypt key in EEPROM.

In normal operation, each received message of valid
format is evaluated. The serial number is used to deter­mine if it is from a learned transmitter. If from a learned
transmitter, the message is decrypted and the synchro­nization counter is verified. Finally, the button status is
checked to see what operation is requested. Figure 1-3
shows the relationship between some of the values
stored by the receiver and the values received from
the transmitter.

 2002 Microchip Technology Inc. DS40152E-page 3

HCS360

FIGURE 1-2: BUILDING THE TRANSMITTED CODE WORD (ENCODER)

EEPROM Array

Crypt Key

Sync Counter

Serial Number

KEELOQ

Encryption

Algorithm

Button Press

Information

Serial Number

Transmitted Information

FIGURE 1-3: BASIC OPERATION OF RECEIVER (DECODER)

1

Received Information

Button Press
Information

Serial Number

Check for

2

Match

32 Bits of

Encrypted Data

32 Bits

Encrypted Data

EEPROM Array

Manufacturer Code

Serial Number

Sync Counte r

KEELOQ
Decryption
Algorithm

Decrypted

Synchronization

Counter

Perform Function
Indicated by

5

button press

NOTE: Circled numbers indicate the order of execution.

Crypt Key

3

Check for

4

Match

DS40152E-page 4  2002 Microchip Technology Inc.

HCS360

2.0 DEVICE OPERATION

As shown in the typical a pplication circ uits (Figu re 2-1),
the HCS360 is a simple device to use. It requires only
the addition of buttons and RF circuitry for use as the
transmitter in your security applic ation. A descripti on of
each pin is described in Table2-1.

FIGURE 2-1: TYPICAL CIRCUITS

VDD

B0

B1

S0
S1

S2
S3

Two button remote control

VDD
LED

DATA

V

SS

Tx out

discrimination value and button information will be
encrypted to form the hopping code. The hopping code
portion will change every transmission, even if the
same button is pushed again. A code word that has
been transmitted will not repeat for more than 64K
transmissions. Thi s provides mo re than 18 years of use
before a code is repeated; based on 10 operations per
day . Overflow inform ation sent from the enc oder can be
used to extend the number of unique transmissions to
more than 192K.

If in the tr an smit proc ess it i s de tec ted t hat a n ew b ut­ton(s) has been pressed, a RESET will immediately
occur and the current cod e word will no t be compl eted.
Please note that buttons removed will not have any
effect on the code word unless no buttons remain
pressed; in which c ase the code word will be compl eted
and the power-down will occur.

FIGURE 2-2: ENCODER OPERATION

TABLE 2-1: PIN DESCRIPTIONS

Name

S0 1 Switch input 0
S1 2 Switch input 1
S2 3 Switc h input 2 / Clock pin when in

S3 4 Switch input 3

SS 5 Ground reference

V

DATA 6 Data output pin /Data I/O pin for

LED
VDD 8 Positive supply voltage

The HCS360 will wake-up upon detecting a button
press and delay approximately 10 ms for button
debounce (Figure 2-2). The synchronization counter,

 2002 Microchip Technology Inc. DS40152E-page 5

Pin

Number

Description

Programming mode

Programming mode

7 Cathode connection for LED

HCS360

3.0 EEPROM MEMORY ORGANIZATION

The HCS360 contains 192 bits (12 x 16-bit words) of
EEPROM memory (Table 3-1). This EEPROM array is
used to store the crypt key information, synchronization
value, etc . Fu r t he r d es cr i pti o ns of t h e m e mory array is
given in the following sections.

TABLE 3-1: EEPROM MEMORY MAP

WORD

ADDRESS

0 KEY_0 64-bit crypt key

1 KEY_1 64-bit crypt key

2 KEY_2 64-bit crypt key

3 KEY_3 64-bit crypt key

4 SYNC_A 16-bit synch counter
5 SYNC_B/

6 RESERVED Set to 0000H
7SEED_0Seed Value

8SEED_1Seed Value

9SER_0Device Serial Number

10 SER_1 Device Serial Number

11 CONFIG Configuration Word

MNEMONIC DESCRIPTION

(word 0) LSb’s

(word 1)

(word 2)

(word 3) MSb’s

16-bit synch counter B

SEED_2

or Seed value (word 2)

(word 0) LSb’s

(word 1) MSb’s

(word 0) LSb’s

(word 1) MSb’s

3.2 SYNC_A, SYNC_B
(Synchronization Counter)

This is th e 16 -bit syn chr oni zatio n va lue th at is used to
create the hopping code for trans missio n. This value is
incremented after every transmission. Separate syn­chronization counters can be used to stay synchro­nized with different receivers.

3.3 SEED_0, SEED_1, and SEED_2
(Seed Word)

The three word (48 bits) seed code will be transmitted
when seed transmission is selected. This allows the sys­tem designer to implement the Secure Learn feature or
use this fixed code word as part of a different key genera­tion/tracking process or purely as a fixed code transmis­sion.

Note: Since SEED2 and SYNC_B share the

same memory location, Secure Learn and
Independent mod e trans miss ion (inclu ding
IR mode) are mutually exclusive.

3.4 SER_0, SER_1
(Encoder Serial Number)

SER_0 and SER_1 are the lower and upper words of
the device serial number, respectively. There are 32
bits allocated for the Serial Number and a selectable
configuration bit determines whether 32 or 28 bits will
be transmitted. The serial number is meant to be
unique for every transmitter.

3.1 KEY_0 - KEY_3 (64-Bit Crypt Key)

The 64-bit crypt key is used to create the encrypted
message transmitted to the receiver. This key is calcu­lated and programmed during production using a key
generation algorithm. The key generation algorithm
may be different from the K
the key generation algorithm are typically the transmit-

ter’s serial number and the 64 -bit manufa cturer’s cod e.
While the key generation algorithm supplied from
Microchip is the typical method used, a user may elec t
to create their own m ethod of key gene ration. This ma y
be done providing that the deco der is program med with
the same means of creating the key for
decryption purposes.

DS40152E-page 6  2002 Microchip Technology Inc.

EELOQ

algorithm. Inputs to

HCS360

3.5 CONFIG
(Configuration Word)

The Configuration Word is a 16-bit word stored in
EEPROM array that is used by the device to store
information used during the enc ryption proce ss, as well
as the status of option configurations. Further
explanations of each of the bits are described in the
following sections.

TABLE 3-2: CONFIGURATION WORD.

Bit Number Symbol Bit Description

0 LNGRD Long Guard Tim e
1 BSEL 0 Baud Rate Selection
2 BSEL 1 Baud Rate Selection
3 NU Not Used
4 SEED Seed Transmission enable
5 DELM Delay mode enable
6 TIMO Time-out enable
7 IND Independent mode enable
8 USRA0 User bit

9 USRA1 User bit
10 USRB0 User bit
11 USRB1 User bit
12 XSER Extended serial number

enable

13 TMPSD Temporary seed transmis-

sion enable

14 MOD Manchester/PWM modula-

tion selection

15 OVR Overflow bit

3.5.1 MOD: MODULATION FORMAT

MOD selects between Manchester code modulation
and PWM modulation.

If MOD = 1, Manchester modulation is selected:
If MOD = 0, PWM modulation is selected.

BSEL 1 and BSEL 0 determine the baud rate according
to Table3-4 when Manchester modulation is selected.

TABLE 3-4: BAUD RATE SELECTION

MOD BSEL 1 BSEL 0 TE Unit

100800us
101400us
110400us
111200us

3.5.3 OVR: OVERFLOW

The overflow bit is u sed to exten d the nu mber o f poss i­ble synchronization values. The synchronization
counter is 16 bits in length, yielding 65,536 values
before the cycle repeats. Under typical use of
10 operations a day, this will provide n ea rly 18 years of
use before a repeated value will be used. Should the
system designer conclude that is not adequate, then
the overflow bit can be utiliz ed to exte nd the numbe r of
unique values. This can be do ne by pr ogramming O VR
to 1 at the time of production. The encoder will auto­matically clear OVR the first time that the transmitted
synchronization value wraps from 0xFFFF to 0x0000.
Once cleared, OVR cannot be set again, thereby crea t­ing a permanent record of the counter overflow. This
prevents fast cycling of 64K counter . If the dec oder sys­tem is programmed to track the overflow bits, then the
effective number of unique synchronization values can
be extended to 128K. If programmed to zero, the sys­tem will be compatible with old encoder devices.

3.5.4 LNGRD: LONG GUARD TIME

LNGRD = 1 selects the encoder to extend the guard
time between code words adding ≈50 ms. This can be
used to reduce the average power transmitted over a
100 ms window and thereby transmit a higher peak
power.

3.5.2 BSEL 1, 0
BAUD RATE SELECTION

BSEL 1 and BSEL 0 determin e the baud rate according
to Table 3-3 when PWM mo dulation is selected.

TABLE 3-3: BAUD RATE SELECTION

MOD BSEL 1 BSEL 0 T

000400us
001200us
010200us
011100us

 2002 Microchip Technology Inc. DS40152E-page 7

E Unit

HCS360

3.5.5 XSER: EXTENDED SERIAL
NUMBER

If XSER = 0, the four Most Significant bits of the Serial
Number are substituted by S[3:0] and the code word
format is co mpatible with the HCS200/300/301.

If XSER = 1, the full 32-bit Serial Number [SER_1,
SER_0] is transmitted.

Note: Since the button status S[3:0] is used to

detect a Seed transmission, Extended
Serial Number and Secure Learn are
mutually exclusive.

FIGURE 3-1: CODE WORD ORGANIZATION

XSER=0

Fixed Code Portion of Transmission Encrypted Portion of Transmission

Button
Status
(4 bits)

28-bit

Serial Number

MSB

CRC

(2-bit)

VLOW
(1-bit)

3.5.6 DISCRIMINATION VALUE

While in other KEELOQ encoders its value is user
selectable, the HCS360 uses directly the 8 Least Sig­nificant bits of the Se rial N umber a s part of t he info r­mation that form the encrypted portion of the
transmission (Figure 3-1).

The discrimination value aids the post-decryption
check on the decoder end. After the receiver has
decrypted a transmiss ion, the discrimination b its are
checked against the e ncoder Serial Number to verif y
that the decryp tion process was valid.

3.5.7 USRA,B: USER BITS

User bits form part of the discrimi nation valu e. The user
bits together with the IND bit can be used to identify the
counter that is used in Independent mode.

Button
Status

(4 bits)

Discrimination

bits

(12 bits)

16-bit

Sync Value

LSB

XSER=1

MSB

Fixed Code Portion of Transmission Encrypted Portion of Transmission

CRC

(2-bit)

VLOW
(1-bit)

Button Status

(4 bits)
SSSS
2103

Extended Serial Number

32-bit

Button
Status

(4 bits)

I O U U S S ... S

N V S S E E ... E

Discrimination

bits

(12 bits)

Discrimination Bits

(12 bits)

D R R R R R ... R

1 0 7 6 ... 0

67 bits
of Data
Transmitted

16-bit

Sync Value

LSB

DS40152E-page 8  2002 Microchip Technology Inc.

HCS360

3.5.8 SEED: ENABLE SEED
TRANSMISSION

If SEED = 0, seed transmission is disabled. The Inde­pendent Counter mode can only be used with seed
transmission disable d since SEED_2 i s shared with th e
second synchronization counter.

With SEED = 1, seed transmission is enabled. The
appropriate button code(s) must be activated to trans­mit the seed information. In this mode, the seed infor-

FIGURE 3-2: Seed Transmission

All examples shown with XSER = 1, SEED = 1

When S[3:0] = 1001, delay is not acceptable.

CRC+VLOW SER_1 SEED_2 SEED_1 SEED_0

For S[3:0] = 0x3 before delay:

CRC+VLOW SER_1 SER_0 Encrypted Data

mation (SEED_0, SEED_1, and SEED_2) and the
upper 12 or 16 bits of the serial number (SER_1) are
transmitted instead of the hop code.

Seed transmission is available for function codes
(Table 3-9) S[3:0] = 1001 and S[3:0] = 0011(delayed).
This takes place regardless of the setting of the IND bit.
The two seed transmissions are shown in Figure 3-2.

Data transmission direction

16-bit Data Word 16-bit Counter

Encrypt

Data transmission direction

For S[3:0] = 0011 after delay (Note 1, Note 2):

CRC+VLOW SER_1 SEED_2 SEED_1 SEED_0

Note 1 : For Seed Transmission, SEED_2 is transmitted instead of SER_0.

2: For Seed Transmission, the setting of DELM has no effect.

3.5.9 TMPSD: TEMPORARY SEED
TRANSMISSION

The temporary seed transmission can be used to dis­able learning after the transmitter has been used for a
programmable number of operations. This feature can
be used to implemen t very secu re systems. After learn­ing is disabled, the seed information cannot be
accessed even if physical access to the transmitter is
possible. If TMPSD = 1 the seed transmission will be
disabled after a number of code hopping transmis­sions. The number of tra nsmiss ions be fore see d trans­mission is disabl ed, can be programmed by setting th e
synchronization counter (SYNC_A, SYNC_B) to a
value as shown in Table 3-5.

Data transmission direction

TABLE 3-5: SYNCHRONOUS COUNTER

INITIALIZATION VALUES

Synchronous Counter

Value s

0000H 128
0060H 64
0050H 32
0048H 16

Number of

Transmissions

 2002 Microchip Technology Inc. DS40152E-page 9

HCS360

3.5.10 DELM: DELAY MODE

If DELM = 1, delay transmission is enabled. A delayed
transmissi on is indic ated by in verting th e lower nib ble
of the discrimination value. The Delay mode is primarily
for compatibil ity with pre vious K
not recommended for new designs.

EELOQ devices and is

TABLE 3-6: TYPICAL DELAY TIMES

Number of Code

BSEL 1 BSEL 0

00 28 ≈ 2.9s ≈ 5.1s
01 56 ≈ 3.1s ≈ 6.4s
10 28 ≈ 1.5s ≈ 3.2s
11 56 ≈ 1.7s ≈ 4.5s

Words before Delay

Mode

3.5.11 TIMO: TIME-OUT
OR AUTO-SHUTOFF

If TIMO = 1, the time-out is enabled. Time-out can be
used to terminate accid ental c ontinuous tran smissions.
When time-out occurs, the PWM output is set low and

TABLE 3-7: TYPICAL TIME-OUT TIMES

If DELM = 0, delay transmission is disabled (Table 3-

6).

Time Before Delay Mode

(MOD = 0)

the LED is turned off. Current consumption will be
higher than in Standby mode since current will flow
through the activated input resistors. This state can be
exited only after al l in put s are taken low. TIMO = 0, will
enable continuous transmission (Table 3-7).

Time Before Delay Mode

(MOD = 1)

Maximum Number of

BSEL 1 BSEL 0

00 256 ≈ 26.5s ≈ 46.9
01 512 ≈ 28.2s ≈ 58.4
10 256 ≈ 14.1s ≈ 29.2
11 512 ≈ 15.7s ≈ 40.7

Code Words
Transmitted

Time Before Time-out

(MOD = 0)

Time Before Time-out

(MOD = 1)

DS40152E-page 10  2002 Microchip Technology Inc.

HCS360

3.5.12 IND: INDEPENDENT MODE

The Independent mode can be used where one

TABLE 3-8: IR MODULATION

T

E Basic Pulse

encoder is used to co ntro l tw o re ce iv ers . Two counters
(SYNC_A and SYNC_B) are used in Independent
mode. As indicated in Table 3-9, function codes 1 to 7
use SYNC_A and 8 to 15 SYNC_B.

800us

(800µs)

(32x)

3.5.13 INFRARED MODE

The Independent mode also selects IR mode. In IR

400us

mode functi on codes 12 to 15 will use SYNC_B. T he
PWM output signal is modulated with a 40 kHz carrier
(see Table 3-8). It must be pointed out that the 40 kHz
is derived from the inte rnal cloc k and wil l therefore vary

200us

(200µs)

with the same percentage as the baud rate. If IND = 0,
SYNC_A is used for all fun ction code s. If IND = 1, Inde­pendent mode is enabled and counters for functions
are used according to Table 3-9.

TABLE 3-9:

FUNCTION CODES

100us

(100µs)

(4x)

S3 S2 S1 S0 IND = 0 IND = 1 Comments

Counter

10001 A A
20010 A A
3 0 0 1 1 A A If SEED = 1, transmit seed after delay.
40100 A A
50101 A A
60110 A A
70111 A A
81000 A B

9 1 0 0 1 A B If SEED = 1, transmit seed immediately.
101010 A B
111011 A B
121100 A

131101 A
141110 A
151111 A

(1)

B

(1)

B

(1)

B

(1)

B

Note 1: IR mode

(400µs)

(16x)

Period = 25µs

(8x)

 2002 Microchip Technology Inc. DS40152E-page 11