HCS300

DS21137F-page 10

© 2001 Microchip Technology Inc.

5.0

SPECIAL FEATURES

5.1

Code Word Completion

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.

5.2

LED Output Operation

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).

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.

5.4

give an indication to the user that the transmitter bat-

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

Section 3.5.1). Setting this bit high will enable the func-

tion (turn Auto-shutoff function on) and setting the bit

low will disable the function. Time-out period is approx-

imately 25 seconds.

5.6

Seed Transmission

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

S2

S1

S0

Standby

0

00

0

0

Hopping Code

1

00

0

1

2

00

1

0

-

--

-

-

13

11

0

1

14

11

1

0

Seed Code

15

11

1

1