HCS300
5.0
5.1
SPECIAL FEATURES
Code Word Completion
5.6
Seed Transmission
The code word completion feature ensures that entire
code words are transmitted, even if the button is
released before the code word is complete. If the but-
ton is held down beyond the time for one code word,
multiple code words will result. If another button is acti-
vated during a transmission, the active transmission
will be aborted and a new transmission will begin using
the new button information.
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 stored in EEPROM, transmitted only
when all four button inputs are pressed at the same
time (Table 5-1). Instead of the normal key generation
inputs being used to create the crypt key, this seed
value is used.
TABLE 5-1:
PIN ACTIVATION TABLE
Function
S3
0
0
0
-
1
1
1
S2
0
0
0
-
1
1
1
S1
0
0
1
-
0
1
1
S0
0
1
0
-
1
0
1
5.2
LED Output Operation
Standby
During normal transmission the LED output is LOW. If
the supply voltage drops below the low voltage trip
point, the LED output will be toggled at approximately
5Hz during the transmission (Section 3.6.4).
0
1
Hopping Code
2
-
13
14
5.3
RPT: Repeat Indicator
This bit will be low for the first transmitted word. If a
button is held down for more than one transmitted code
word, this bit will be set to indicate a repeated code
word and remain set until the button is released.
Seed Code
15
5.4
V
LOW
: Voltage LOW Indicator
The V
LOW
signal is transmitted so the receiver can
give an indication to the user that the transmitter bat-
tery is low. The V
LOW
bit is included in every transmis-
sion (Figure 4-2 and Figure 8-4) and will be
transmitted as a zero if the operating voltage is above
the low voltage trip point. Refer to Figure 4-2. The trip
point is selectable based on the battery voltage being
used. See Section 3.6.3 for a description of how the
low voltage trip point is configured.
5.5
Auto-shutoff
The Auto-shutoff function automatically stops the
device from transmitting if a button inadvertently gets
pressed for a long period of time. This will prevent the
device from draining the battery if a button gets
pressed while the transmitter is in a pocket or purse.
This function can be enabled or disabled and is
selected by setting or clearing the Auto-shutoff bit (see
tion (turn Auto-shutoff function on) and setting the bit
low will disable the function. Time-out period is approx-
imately 25 seconds.
DS21137F-page 10
©
2001 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
