hcs500 Microchip Technology Inc., hcs500 Datasheet - Page 8

• Manufacturer Part Number: hcs500
• Description: Keeloq Code Hopping Decoder
• Manufacturer: Microchip Technology Inc.

HCS500
4.0
The HCS500 interfaces to a microcontroller via a syn-
chronous serial interface. A clock and data line are
used to communicate with the HCS500. The microcon-
troller controls the clock line. There are two groups of
data transfer messages. The first is from the decoder
whenever the decoder receives a valid transmission.
The decoder signals reception of a valid code by taking
the data line high (maximum of 500 ms) The microcon-
troller then services the request by clocking out a data
string from the decoder. The data string contains the
function code, the status bit, and block indicators. The
second is from the controlling microcontroller to the
decoder in the form of a defined command set.
Figure 4-1 shows the HCS500 decoder and the I/O
interface lines necessary to interface to a microcontrol-
ler.
4.1
The decoder informs the microcontroller of a valid
transmission by taking the data line high for up to
500 ms. The controlling microcontroller must acknowl-
FIGURE 4-1:
FIGURE 4-2:
DS40153C-page 8
S_CLK
S_DAT
A
1
2
3
4
INTERFACING TO A
MICROCONTROLLER
Valid Transmission Message
Decoder Signal Valid
A0
A1
A2
Vss
T
CLA
Transmission
T
DHI
T
PP
HCS500 DECODER AND I/O INTERFACE LINES
24LC02
DECODER VALID TRANSMISSION MESSAGE
1
T
CLKH
T
PP
3
B
SCL
Vcc
WP
SD
0
REPT V
8
7
6
5
T
CLKL
V
LOW
DD
S0
1K
T
CLKH
S1
1
2
3
4
V
EE_CLK
EE_DAT
MCLR
S2
DD
Information
S3
HCS500
T
1
DS
edge by taking the clock line high. The decoder then
takes the data line low. The microcontroller can then
begin clocking a data stream out of the HCS500. The
data stream consists of:
• START bit ‘0’.
• 2 status bits [REPEAT, VLOW].
• 4-bit function code [S3 S2 S1 S0].
• STOP bit ‘1’.
• 4 bits indicating which block was used
• 4 bits indicating the number of transmitters
• 64 bits of the received transmission with the hop-
The decoder will terminate the transmission of the data
stream at any point where the clock is kept low for
longer than 1 ms. Therefore, the microcontroller can
only clock out the required bits. A maximum of 80 bits
can be clocked out of the decoder.
CNT0
[TX3…TX0].
learned into the decoder [CNT3…CNT0].
ping code decrypted.
Note:
S_CLK
S_DAT
RFIN
Vss
CNT3
Data is always clocked in/out Least
Significant Bit (LSB) first.
8
7
6
5
TX0
TX3
Ci
2002 Microchip Technology Inc.
RX0
Received String
RX1
MICRO RESET
RF RECEIVER
SYNC CLOCK
SYNC DATA
RX62
RX63
Cii