hcs200 Microchip Technology Inc., hcs200 Datasheet - Page 7

• Manufacturer Part Number: hcs200
• Description: K L Code Hopping Encoder
• Manufacturer: Microchip Technology Inc.

checked against the receiver’s stored value to verify
that the decryption process was valid. If the discrimi-
nation value was programmed as the 12 LSb’s of the
serial number then it may merely be compared to the
respective bits of the received serial number; saving
EEPROM space.
3.6.2
BSL0 selects the speed of transmission and the code
word blanking. Table 3-3 shows how the bit is used to
select the different baud rates and Section 5.2 provides
detailed explanation in code word blanking.
TABLE 3-3:
3.6.3
The low voltage trip point select bit tells the HCS200
what V
used by the device to determine when to send the volt-
age low signal to the receiver. When this bit is set to a
one, the V
9.0 volt or 12.0 volt V
the V
Figure 3-1 for voltage trip point.
FIGURE 3-1:
BSL0
2002 Microchip Technology Inc.
Volts (V)
0
1
DD
DD
level is assumed to be 6.0 volts. Refer to
level is being used. This information will be
DD
5.5
5.0
4.5
4.0
3.5
3.0
2.5
BAUD RATE SELECT BIT (BSL0)
LOW VOLTAGE TRIP POINT
SELECT (V
9.0
8.5
8.0
7.5
7.0
level is assumed to be operating from a
-40
Basic Pulse
Element
400 s
200 s
BAUD RATE SELECT
-20
DD
VOLTAGE TRIP POINTS
BY CHARACTERIZATION
0
LOW SEL
Temp (C)
level. If the bit is set to zero,
20 40
V
V
LOW SEL
LOW SEL
60 80
)
Code Words
Transmitted
= 0
= 1
1 out of 2
100
All
Max
Max
Min
Min
V
LOW
4.0
4.1
The HCS200 code word is made up of several parts
(Figure 4-1). Each code word contains a 50% duty
cycle preamble, a header, 32 bits of encrypted data and
34 bits of fixed data followed by a guard period before
another code word can begin. Refer to Table 8-3 for
code word timing.
4.2
The HCS200 transmits a 66-bit code word when a
button is pressed. The 66-bit word is constructed from
a Fixed Code portion and an Encrypted Code portion
(Figure 4-2).
The 32 bits of Encrypted Data are generated from 4
button bits, 12 discrimination bits and the 16-bit sync
value. The encrypted portion alone provides up to four
billion changing code combinations.
The 34 bits of Fixed Code Data are made up of 1 sta-
tus bit, 1 fixed bit, 4 button bits and the 28-bit serial
number. The fixed and encrypted sections combined
increase the number of code combinations to 7.38 x
10
4.3
Synchronous Transmission mode can be used to clock
the code word out using an external clock.
To enter Synchronous Transmission mode, the Pro-
gramming mode start-up sequence must be executed
as shown in Figure 4-3. If either S1 or S0 is set on the
falling edge of S2, the device enters Synchronous
Transmission mode. In this mode it functions as a nor-
mal transmitter, with the exception that the timing of the
PWM data string is controlled externally and that 16
extra reserved bits are transmitted at the end of the
code word. The reserved bits can be ignored. The but-
ton code will be the S0, S1 value at the falling edge of
S2. The timing of the PWM data string is controlled by
supplying a clock on S2 and should not exceed 20 kHz.
When in Synchronous Transmission mode S2 should
not be toggled until all internal processing has been
completed as shown in Figure 4-3.
19
.
TRANSMITTED WORD
Code Word Format
Code Word Organization
Synchronous Transmission Mode
HCS200
DS40138C-page 7