HCS473 datasheet(16/68 Pages) MICROCHIP

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HCS473

DS40035C-page 14

Preliminary

 2002 Microchip Technology Inc.

3.1.4

ENCODER MODE OPTIONS

The following HCS473 configuration options configure

transmission characteristics of the information exiting

the DATA pin:

• Modulation select (MSEL)

• Header select (HSEL)

• Extended serial number (XSER)

• Queue counter enable (QUEN)

• Counter select (CNTSEL)

• Low voltage trip point (VLOWSEL)

• PLL interface select (AFSK)

• RF enable output (RFEN)

• Seed button code (SDBT)

• Time before Seed (SDTM)

• Limited Seed (SDLM)

• Seed mode (SDMD)

• RF baud rate select (RFBSL)

• Guard time select (GSEL)

• Minimum code words (MTX)

• Timeout select (TSEL)

• Long preamble enable (LPRE)

• Long preamble length (LPRL)

• Preamble duty cycle (PRD)

The following sections detail each configuration’s avail-

able options. All timing values specified are subject to

the specified oscillator variation.

3.1.4.1

Modulation Format (MSEL)

The Modulation format option selects the modulation

format for data output from the DATA pin; most often

transmitted via RF.

MSEL options:

• Pulse Width Modulation (PWM), Figure 3-3

• Manchester Modulation, Figure 3-4

3.1.4.2

Header Select (HSEL)

The synchronization header is typically used by the

receiver to adjust bit sampling appropriate to the trans-

mitter’s current speed; as the transmitter’s RC oscilla-

tor varies with temperature and voltage, so will the

transmission’s timing.

HSEL options:

•4 RF

• 10 RF

3.1.4.3

Extended Serial Number (XSER)

The Extended Serial Number option determines

whether the HCS473 transmits a 28 or 32-bit serial

number.

When configured for a 28-bit serial number, the Most

Significant nibble of the 32 bits reserved for the serial

number is replaced with a copy of the 4-bit button sta-

tus, Figure 3-2.

XSER options:

• 28-bit serial number

• 32-bit serial number

3.1.4.4

Queue Counter (QUEN)

The QUE counter can be used to request secondary

decoder functions using only a single transmitter but-

ton. Typically a decoder must keep track of incoming

transmissions to determine when a double button press

occurs, perhaps an unlock all doors request. The QUE

counter removes this burden from the decoder by

counting multiple button presses and including the

QUE counter value in the last two bits of the 69-bit code

word, (Figure 3-2). If QUEN is disabled, the transmis-

sion will consist only of 67 bits as the QUE bits field is

not transmitted.

Que counter functionality is enabled with the QUEN

configuration option. The 2-bit QUE counter is incre-

mented each time an active button input is released for

at least the Debounce Time (T

DB), then re-activated

(button pressed again) within the Queue Time (T

QUE),

Figure 3-5. The counter increments up from 0 to a max-

imum of 3, returning to 0 only after a different button

activation or after button activations spaced greater

than the Queue Time (T

QUE) apart.

The current transmission aborts, after completing the

minimum number of code words (Section 3.1.4.15),

when the active button inputs are released. A button re-

activation within the queue time (T

QUE) then initiates a

new

transmission

(new

synchronization

counter,

encrypted data) using the updated QUE value. Button

combinations are queued the same as individual but-

tons.

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