HCS512 Datasheet, PDF (5/20 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
according to Table 3-1 when a new valid code is
received. The outputs will be activated for approxi-
mately 500 ms. If a repeated code is received during
this time, the output extends for approximately 500 ms.
TABLE 3-1: FUNCTION OUTPUT TABLE
Function
Code
S3
S2
S1
S0
0001
0
0
0
1
0010
0
0
1
0
0011
0
0
1
1
0100
0
1
0
0
0101
0
1
0
1
0110
0
1
1
0
0111
0
1
1
1
1000
1
0
0
0
1001
1
0
0
1
1010
1
0
1
0
1011
1
0
1
1
1100
1
1
0
0
1101
1
1
0
1
1110
1
1
1
0
1111
1
1
1
1
FIGURE 3-1: DATA OUTPUT FORMAT
START
S3
S2
S1
S0
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 indi-
cate 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.
A special status message is transmitted on the second
pass of learn. This allows the controlling microcontroller
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 3-2 show the values for TX1:0 and the number of
transmitters learned.
TABLE 3-2: STATUS BITS
TX1
TX0 Number of Transmitters
0
0
One
0
1
1
0
1
1
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 and stop bits are ‘1’.
FIGURE 3-3: PWM TRANSMISSION FORMAT
600µs
CLK
DATA
Start
S3
S2
S1
S0 VLOW RPT Reserved Reserved Stop
1200µs
“1”
“0”
© 1997 Microchip Technology Inc.
DS40151C-page 5