HCS320 Datasheet, PDF (13/32 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

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.
HCS320
TABLE 5-1: PIN ACTIVATION TABLE
SHIFT
S2
S1
S0
LEVEL
FUNCTION
CODE
0
0
0
0 No Transmission
0
0
0
1
0h
0
0
1
0
1h
0
0
1
1
2h
0
1
0
0
3h
1
0
0
0 No Transmission
1
0
0
1
4h
1
0
1
0
5h
1
0
1
1
6h
1
1
0
0
7h
2
0
0
0 No Transmission
2
0
0
1
8h
2
0
1
0
9h
2
0
1
1
Ah
2
1
0
0
Bh
3
0
0
0 No Transmission
3
0
0
1
Ch
3
0
1
0
Dh
3
0
1
1
Eh
3
1
0
0
Fh
© 2001 Microchip Technology Inc.
DS41097C-page 13