HCS370IP datasheet(17/36 Pages) MICROCHIP

17 / 36 page

2002 Microchip Technology Inc.

Preliminary

DS41111D-page 17

HCS370

FIGURE 5-2:

LED OPERATION

5.4

Step-Up Voltage Regulator

To create your own step-up regulator circuit, first decide

on an output voltage. Second, set the VIN resistor

divider to drop it down to 1.2 volts. Keep the sum of the

two resistors around 100 k

Ω. Third, put your maximum

load on the output and increase the inductance until

COUT charges from 0 volts to your output voltage in

about 30 ms from the minimum input voltage. Finally,

test over your temperature and input voltage ranges.

The WAIT option will delay RF transmissions until

COUT is charged. This permits a trade off in slower but-

ton response times to save money on cheaper induc-

tors. This can also optimize performance for good

batteries and let response times drift for weak batteries.

Also, this option will indicate failure to reach regulation

voltage after 250 ms by not transmitting and not flash-

ing the LED. If WAIT is disabled, the step-up regulator

still operates and transmissions will always start 30 ms

after a button press.

The SLEEP Output Enable (SOEN) option can be

enabled if S5 is not used. This reconfigures S5 to be an

output high when the HCS370 is sleeping. S5 will be an

output low when a button press wakes it up. One way

to use this option is to save power on the step-up reg-

ulator. The problem is that the VIN resistor divider

makes a DC path through the inductor and diode to dis-

charge the battery. By tying the bottom of the divider to

SLEEP as shown in Figure 2-1, the path is broken

between transmissions.

5.5

Cyclic Redundancy Check (CRC)

The CRC bits are calculated on the 65 previously trans-

mitted bits. These bits contain the 32-bit hopping code,

32-bit fixed code, and VLOW bit. The decoder can use

the CRC bits to check the data integrity before process-

ing starts. The CRC can detect all single bit errors and

66% of double bit errors. The CRC is computed as fol-

lows:

EQUATION 5-1:

CRC Calculation

and

with

and Di

n the nth transmission bit 0 <= n <= 64

5.6

Button Queue Information

(QUEUE)

The queuing or repeated pressing of the same buttons

can be handled in two ways on the HCS370. This is

controlled with the Queue Counter Enable (QUEN)

configuration option. This option can be different for

Encoder 1 and Encoder 2.

When the QUEN option is disabled, the device will reg-

ister up to two sequential button presses. In this case,

the device will complete the minimum code words

selected with the MTX option before the second code

word is calculated and transmitted. The code word will

be 67 bits in this case, with no additional queue bits

transmitted.

If the QUEN option is enabled, the queue bits are

added to the standard code word. The queue bits are a

2-bit counter that does not wrap. The counter value

starts at 00

2 and is incremented if a button is pushed

within 2 seconds from the start of the previous button

press. The current code word is terminated when a but-

ton is queued. This allows additional functionality for

double or triple button presses.

FIGURE 5-3:

CODE WORD COMPLETION

WITH QUEN SETTINGS

6.0

PROGRAMMING

SPECIFICATIONS

Refer to the “HCS370 Programming Specifications”

document (DS41157) in Microchip Literature.

LED

VDD > VLOW

VDD < VLOW

TLEDON

TLEDOFF

LEDBL=1

LED

VDD < VLOW

LEDBL=0

CRC 1

[]

CRC 0

[]

⊕

CRC 0

[]

CRC 0

[]

⊕

() CRC 1

[]

⊕

CRC 1 0

[]

QUEN = Disabled

QUEN = Enabled

DATA

WAKE-UP

CODE2

MTX = 01

2, WAKE > 002

CODE1

WAKE-UP

DATA

WAKE-UP

CODE1

WAKE-UP

CODE2 01

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