HCS512_02 Datasheet, PDF (5/26 Pages) Microchip Technology – KEELOQ® Code Hopping Decoder

HCS512
3.0 DESCRIPTION OF FUNCTIONS
3.1 Parallel Interface
The HCS512 activates the S3, S2, S1 & S0 outputs
when a new valid code is received. The outputs will be
activated for approximately 500 ms. If a repeated code
is received during this time, the output extends for
approximately 500 ms.
3.2 Serial Interface
The decoder has a PWM/Synchronous interface con-
nection to microcontrollers with limited I/O. An output
data stream is generated when a valid transmission is
received. The data stream consists of one START bit,
four function bits, one bit for battery status, one bit to
indicate a repeated transmission, two status bits, and
one STOP bit. (Table 3-1). The DATA and CLK lines are
used to send a synchronous event message.
FIGURE 3-1: DATA OUTPUT FORMAT
START
S3
S2
S1
S0
A special status message is transmitted on the second
pass of learn. This allows the controlling microcontrol-
ler to determine if the learn was successful (Result = 1)
and if a previous transmitter was overwritten (Overwrite
= 1). The status message is shown in Figure 3-2.
Table 3-1 show the values for TX1:0 and the number of
transmitters learned.
TABLE 3-1: STATUS BITS
TX1
TX0 Number of Transmitters
0
0
0
1
1
0
1
1
One
Two
Three
Four
VLOW
REPEAT
TX1
TX0 STOP
FIGURE 3-2: STATUS MESSAGE FORMAT
START
0
0
0
0
RESULT _{OVRWR TX1}
TX0 STOP
A 1-wire PWM or 2-wire synchronous interface can be used.
In 1-wire mode, the data is transmitted as a PWM signal with a basic pulse width of 400 µs.
In 2-wire mode, Synchronous mode PWM bits start on the rising edge of the clock, and the bits must be sampled on the
falling edge. The START bit is a ‘1’ and the STOP bit is ‘0’.
FIGURE 3-2: PWM OUTPUT FORMAT⁽¹⁾
1/31/3 1/3
LOGIC “1”
600 µs
LOGIC “0”
1200 µs
CLK
DATA
START
S3
S2
S1
S0
VLOW RPT Reserved Reserved STOP
1200 µs
Note: The Decoder output PWM format logic (“1” / “0”) is reversed with respect of the Encoder modulation format.
© 2002 Microchip Technology Inc.
DS40151D-page 5