HCS320 datasheet(13/32 Pages) MICROCHIP

13 / 32 page

DS41097C-page 13

HCS320

5.7

SHIFT Key Operation

The HCS320 has four switch inputs usually connected

to buttons as shown in Figure 2-1: Typical Circuits.

Any button connected to input S0, S1 or S2 is called a

TRANSMIT button as it causes a transmission when

pressed.

The SHIFT button is connected to the SHIFT input.

Pressing the SHIFT button increments a counter by

one count and does not result in a transmission. The

counter value is called the shift level. Successive

presses of the SHIFT button can increase the shift level

up to three before wrapping back to zero. The shift level

is available for eight seconds when the SHIFT button is

released, after which the shift level is reset to zero.

When a TRANSMIT button is pressed, the function

code transmitted for that button depends on the shift

level. The transmitted function code corresponding to

shift level and S0, S1 and S2 switch activation is shown

in Table 5-1 for all legal combinations of shift level and

button input. Note that a shift level of zero means that

the SHIFT button has not been pressed (or it has been

pressed four times). The shift level is reset to zero after

a transmission.

The volatile nature of the shift level register requires the

HCS320 to be powered continuously for correct opera-

tion and not powered via the buttons.

TABLE 5-1:

PIN ACTIVATION TABLE

SHIFT

LEVEL

FUNCTION

CODE

000

No Transmission

001

010

011

100

000

No Transmission

001

010

011

100

000

No Transmission

010

011

100

000

No Transmission

001

010

011

100

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