HCS200_11 Datasheet, PDF (10/34 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder 32-bit hopping code

HCS200
6.0 PROGRAMMING THE HCS200
When using the HCS200 in a system, the user will have
to program some parameters into the device, such as
the serial number and crypt key, before it can be used.
The programming cycle allows the user to input all 192
bits in a serial data stream, which are then stored inter-
nally in EEPROM. Programming will be initiated by
forcing the PWM line high, after the S2 line has been
held high for the appropriate length of time (Table 6-1
and Figure 6-1). After the Program mode is entered, a
delay must be provided for the automatic bulk write
cycle to complete. This will write all locations in the
EEPROM to zeros. The device can then be pro-
grammed by clocking in 16 bits at a time, using S2 as
the clock line and PWM as the data in line; data is
clocked in on the falling edge of S2. After each 16-bit
word is sent, a programming delay of TWC is required
for the internal program cycle to complete. At the end
of the programming cycle, the device can be verified
(Figure 6-2) by reading back the EEPROM. Reading is
done by clocking the S2 line and reading the data bits
on PWM. The falling edge of S2 initiates the reading.
For security reasons, it is not possible to execute a Ver-
ify function without first programming the EEPROM. A
Verify operation can only be done immediately fol-
lowing the Program cycle.
Note:
To ensure that the device does not acci-
dentally enter Programming mode (result-
ing in a bulk erase), PWM should never be
pulled high by the circuit connected to it.
Special care should be taken when driving
PNP RF transistors.
FIGURE 6-1:
PROGRAMMING WAVEFORMS
Enter Program
Mode
TPBW
TCLKH
TDS
S2
(Clock)
PWM
(Data)
TPS TPH1
TCLKL
TDH
Bit 0 Bit 1 Bit 2 Bit 3
Bit 14 Bit 15
TWC
Bit 16 Bit 17
TPH2
Data for Word 0 (KEY_0)
Repeat for each word (12 times)
Note 1: Unused button inputs to be held to ground during the entire programming sequence.
2: The VDD pin must be taken to ground after a Program/Verify cycle.
Data for Word 1
FIGURE 6-2:
VERIFY WAVEFORMS
End of Programming Cycle Beginning of Verify Cycle
PWM
(Data)
Bit190 Bit191
S2
(Clock)
TWC
Data from Word 0
Bit 0
Bit 1 Bit 2 Bit 3
TDV
Bit 14
Bit 15
Bit 16 Bit 17
Note: If a Verify operation is to be done, then it must immediately follow the Program cycle.
Bit190 Bit191
DS40138D-page 10
© 2011 Microchip Technology Inc.