HCS200-ISN MICROCHIP [Microchip Technology], HCS200-ISN Datasheet - Page 8

• Manufacturer Part Number: HCS200-ISN
• Description: KEELOQ CODE HOPPING ENCODER
• Manufacturer: MICROCHIP [Microchip Technology]

HCS200
5.0
5.1
Code word completion is an automatic feature that
makes sure that the entire code word is transmitted,
even if the button is released before the transmission is
complete. The HCS200 encoder powers itself up when
a button is pushed and powers itself down after the
command is finished, if the user has already released
the button. If the button is held down beyond the time
for one transmission, then multiple transmissions will
result. If another button is activated during a
transmission, the active transmission will be aborted
and the new code will be generated using the new
button information.
5.2
Federal Communications Commission (FCC) part 15
rules specify the limits on fundamental power and
harmonics that can be transmitted. Power is calculated
on the worst case average power transmitted in a
100 ms window. It is therefore advantageous to
minimize the duty cycle of the transmitted word. This
can be achieved by minimizing the duty cycle of the
individual bits and by blanking out consecutive words.
Blank Alternate Code Word (BACW) is used for
reducing the average power of a transmission
(Figure 5-1). This is a selectable feature that is
determined in conjunction with the baud rate selection
bit BSL0. Using the BACW allows the user to transmit a
higher amplitude transmission if the transmission
length is shorter. The FCC puts constraints on the aver-
FIGURE 5-1:
TABLE 5-1:
DS40138A-page 8
Standby after CC
Fixed
(1 out of 2 transmitted)
(All words transmitted)
BACW Disabled
BACW Enabled
Hop
SPECIAL FEATURES
Code Word Completion
Blank Alternate Code Word
External
BLANK ALTERNATE CODE WORD (BACW)
PIN ACTIVATION TABLE
S2
0
0
0
1
1
1
1
0
S1
2A
0
1
1
0
0
1
1
Amplitude
0
A
S0
0
1
0
1
0
1
0
1
100ms
S3
0
0
0
1
1
1
0
1
Preliminary
S2
0
0
0
1
1
1
1
0
Internal
100ms
age power that can be transmitted by a device, and
BACW effectively prevents continuous transmission by
only allowing the transmission of every second word.
This reduces the average power transmitted and
hence, assists in FCC approval of a transmitter device.
5.3
In order to increase the level of security in a system, it is
possible for the receiver to implement what is known as
a secure learn function. This can be done by utilizing the
seed value on the HCS200 which is stored in EEPROM
and can only be transmitted when all three button inputs
are pressed at the same time (Table 5-1). Instead of the
normal key generation method being used to create the
encryption key, this seed value is used.
5.4
The V
(Figure 4-2 and Figure 8-5) and will be transmitted as a
zero if the operating voltage is above the voltage trip
point. The V
can give an indication to the user that the transmitter
battery is low.
S1
0
0
1
1
0
1
1
1
LOW
One Code Word
S0
Seed Transmission
V
0
1
0
1
0
0
0
1
LOW
bit is transmitted with every transmission
LOW
100ms
: Voltage LOW indicator
signal is transmitted so the receiver
1996 Microchip Technology Inc.
100ms