hcs515 Microchip Technology Inc., hcs515 Datasheet - Page 9

• Manufacturer Part Number: hcs515
• Description: Keeloq Code Hopping Decoder Keeloq Code Hopping Decoder
• Manufacturer: Microchip Technology Inc.

4.2
4.2.1
The microcontroller command consists of four parts.
The first part activates the Command mode, the sec-
ond part is the actual command, the third is the address
accessed, and the fourth part is the data. The micro-
controller starts the command by taking the clock line
high for up to 500 ms. The decoder acknowledges the
start-up sequence by taking the data line high. The
microcontroller takes the clock line low, after which the
decoder will take the data line low, tri-state the data line
and wait for the command to be clocked in. The data
must be set up on the rising edge and will be sampled
on the falling edge of the clock line.
FIGURE 4-3:
2002 Microchip Technology Inc.
HCS515
C Data
Data
CLK
Command Mode
A
MICROCONTROLLER COMMAND
MODE ACTIVATION
T
T
START Command
REQ
RESP
MICROCONTROLLER COMMAND MODE ACTIVATION
T
START
T
ACK
B
LSB
T
CLKL
Command Byte
T
CLKH
MSB
T
CMD
T
DS
C
LSB
4.2.2
The HCS515 uses collision detection to prevent
clashes between the decoder and microcontroller.
Whenever the decoder receives a valid transmission
the following sequence is followed:
• The decoder first checks to see if the clock line is
• The decoder takes the data line high and checks
• If the clock line goes high after 50 s but before
• The microcontroller can then start to clock out the
high. If the clock line is high, the valid transmis-
sion notification is aborted, and the microcontrol-
ler Command mode request is serviced.
that the clock line doesn’t go high within 50 s. If
the clock line goes high, the valid transmission
notification is aborted and the Command mode
request is serviced.
500 ms, the decoder will acknowledge by taking
the data line low.
80-bit data stream of the received transmission.
Address Byte
MSB
COLLISION DETECTION
T
ADDR
D
LSB
Data Byte
HCS515
MSB
DS40183D-page 9
T
DATA
E