HCS500 datasheet(13/40 Pages) MICROCHIP

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DS40153D-page 13

HCS500

4.2.8

ERASE ALL

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

Stand-alone Mode

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

Erase All Command and Erase

Command

The Table 4-3 describes two versions of the Erase All

command.

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

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:

Programming of the manufacturer’s code.

Erasing of all transmitters

(subcommand 00 only).

4.5

Test mode

A special test mode is activated after:

Programming of the manufacturer’s code.

Erasing of all transmitters.

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:

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).

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

Power Supply Supervisor

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.

Note:

The REPS bit must be cleared in the con-

figuration byte in Stand-alone mode.

TABLE 4-3:

ERASE ALL COMMAND

Command

Byte

Subcommand

Byte

Description

C316

0016

Erase all

transmitters.

C316

0116

Erase all transmit-

ters except 1. The

first transmitter in

memory is not

erased.

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