hcs500 Microchip Technology Inc., hcs500 Datasheet - Page 13

• Manufacturer Part Number: hcs500
• Description: Keeloq Code Hopping Decoder
• Manufacturer: Microchip Technology Inc.

4.2.8
The erase all command (Figure 4-9) erases all the
transmitters in the decoder. After the command and two
dummy bytes are clocked in, the clock line must be
asserted to activate the command. After a successful
completion of an erase all command, the data line is
asserted until the clock line goes low.
4.3
The HCS500 decoder can also be used in stand-alone
applications. The HCS500 will activate the data line for
up to 500 ms if a valid transmission was received, and
this output can be used to drive a relay circuit. To acti-
vate learn or erase all commands, a button must be
connected to the CLK input. User feedback is indicated
on an LED connected to the DATA output line. If the
CLK line is pulled high, using the learn button, the LED
will switch on. After the CLK line is kept high for longer
than 2 seconds, the decoder will switch the LED line off,
indicating that learn will be entered if the button is
released. If the CLK line is kept high for another 6 sec-
onds, the decoder will activate an ERASE_ALL Com-
mand.
Learn mode can be aborted by taking the clock line
high until the data line goes high (LED switches on).
During learn, the data line will give feedback to the user
and, therefore, must not be connected to the relay drive
circuitry.
After taking the clock low and before a transmitter is
learn, any low-to-high change on the clock line may ter-
minate learn. This has learn implications when a switch
with contact bounce is used.
4.4
The Table 4-3 describes two versions of the Erase All
command.
TABLE 4-3:
Subcommand 01 can be used where a transmitter with
permanent status is implemented in the microcontroller
software. Use of subcommand 01 ensures that the per-
manent transmitter remains in memory even when all
Note:
2002 Microchip Technology Inc.
Command
Byte
C3
C3
16
16
Stand-alone Mode
Erase All Command and Erase
Command
The REPS bit must be cleared in the con-
figuration byte in Stand-alone mode.
ERASE ALL
Subcommand
ERASE ALL COMMAND
Byte
00
01
16
16
Erase all
transmitters.
Erase all transmit-
ters except 1. The
first transmitter in
memory is not
erased.
Description
other transmitters are erased. The first transmitter
learned after any of the following events is the first
transmitter in memory and becomes the permanent
transmitter:
1.
2.
4.5
A special test mode is activated after:
1.
2.
Test mode can be used to test a decoder before any
transmitters are learned on it. Test mode enables test-
ing of decoders without spending the time to learn a
transmitter. Test mode is terminated after the first suc-
cessful learning of an ordinary transmitter. In test
mode, the decoder responds to a test transmitter. The
test transmitter has the following properties:
1.
2.
3.
4.
Because the synchronization counter value is ignored
in test mode, any number of test transmitters can be
used, even if their synchronization counter values are
different.
4.6
Reliable operation of the HCS500 requires that the
contents of the EEPROM memory be protected against
erroneous writes. To ensure that erroneous writes do
not occur after supply voltage “brown-out” conditions,
the use of a proper power supply supervisor device
(like Microchip part MCP100-450) is imperative.
Programming of the manufacturer’s code.
Erasing of all transmitters
(subcommand 00 only).
Programming of the manufacturer’s code.
Erasing of all transmitters.
crypt key = manufacturer’s code.
Serial number = any value.
Discrimination bits = lower 10 bits of the serial
number.
Synchronization counter value = any value
(synchronization information is ignored).
Test mode
Power Supply Supervisor
HCS500
DS40153C-page 13