HCS370P datasheet(12/36 Pages) MICROCHIP

12 / 36 page

HCS370

DS41111D-page 12

Preliminary

2002 Microchip Technology Inc.

FIGURE 3-2:

CODE WORD DATA FORMAT (20-BIT COUNTER)

3.2.3.1

Low Voltage Detector Status (VLOW)

A low battery voltage detector onboard the HCS370

can indicate when the operating voltage drops below a

predetermined value. There are two options available

depending on the Low Voltage Trip Point Select

(VLOWSEL) configuration option. The two options pro-

vided are:

• A 2.2V nominal level for 3V operation

• A 3.2V nominal level for 5V operation

The output of the low voltage detector is checked on

the first preamble pulse of each code word with the

LED momentarily turned off. The VLOW bit is transmit-

ted in each code word so the decoder can give an indi-

cation to the user that the transmitter battery is low.

Operation of the LED changes as well to further indi-

cate that the battery is low and needs replacing.

The output of the Low Voltage Detector can also be

latched once it has dropped below the selected value.

The Low Voltage Latch (VLOWL) configuration option

enables this option. If this option is enabled, the detec-

tor level is raised to 3V or 5V once a low battery voltage

has been detected, like a Schmitt Trigger.

This will effectively hold the VLOW bit high until the bat-

tery is replaced. If the Low Voltage Latch is enabled,

then the low TE after the first preamble pulse can

stretch by 4 ms one time as the latch changes state.

Transmission Direction LSB First

Fixed Code Portion (32 Bits)

QUE

2 Bits

CRC

2 Bits

VLOW

1-Bit

SERIAL NUMBER

(28 Bits)

Q1 Q0 C1 C0

S2 S1 S0

BUT

4 Bits

DISC

8 Bits

Synchronization

20 Bits

Counter

S0 S3

Hopping Code Portion (32 Bits)

With XSER=0, 20-bit Counter, QUEN=1

Status Information

(5 Bits)

BUT

4 Bits

Fixed Code Portion (32 Bits)

CRC

2 Bits

VLOW

1-Bit

SERIAL NUMBER

(32 Bits)

C1 C0

BUT

4 Bits

DISC

8 Bits

Synchronization

20 Bits

Counter

S0 S3

Hopping Code Portion (32 Bits)

With XSER=1, 20-bit Counter, QUEN=0

Status Information

(3 Bits)

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