HCS320 Datasheet, PDF (11/32 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

HCS320
5.0 SPECIAL FEATURES
5.1 Code Word Completion
Code word completion is an automatic feature that
makes sure that the entire code word is transmitted,
even if the transmit button is released before the trans-
mission is complete. The HCS320 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 function new code will be generated
using the new button information.
5.2 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
(Section 3.4.1). Setting this bit high will enable the
function (turn Auto-shutoff function on) and setting the
bit low will disable the function. Time-out period is
dependent on the shift level and is approximately 42
±10 seconds.
5.3 VLOW: Voltage LOW Indicator
The VLOW bit is transmitted with every transmission
(Figure 8-6) and will be transmitted as a one if the oper-
ating voltage has dropped below the low voltage trip
point. The trip point is selectable between two values,
based on the battery voltage being used. See
Section 3.5.4 for a description of how the low voltage
select option is set. This VLOW signal is transmitted so
the receiver can alert the user that the transmitter bat-
tery is low.
Note:
Depending on the internal resistance of the
VDD source, VDD may normally be above
the VLOW trip point except when the LED is
turned on. In this case, the VLOW bit will be
transmitted as a one when a transmission
occurs while the LED is on. The VLOW bit
will be transmitted as a zero when a trans-
mission occurs while the LED is off.
5.4 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.
5.5 LED Output Operation
During normal transmission the LED output (Figure 5-1)
indicates the shift level (Section 5.7) by flashing the
LED in a pattern corresponding to the shift level. If the
supply voltage drops below the low voltage trip point
(Section 3.5.4), the LED output will be toggled at
approximately 5 Hz during the transmission.
FIGURE 5-1:
SHIFT
LEVEL
0
LED FLASH FUNCTION (EACH DIVISION - 180 MS)
LED OUTPUT
1
2
3
© 2001 Microchip Technology Inc.
DS41097C-page 11