HCS201 Datasheet, PDF (13/28 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

HCS201
6.0 PROGRAMMING THE HCS201
When using the HCS201 in a system, the user will have
to program some parameters into the device including
the serial number and the secret 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 internally in EEPROM. Programming will be
initiated by forcing the DATA line high, after the S2 line
has been held high for the appropriate length of time
line (Table 6-1 and Figure 6-1). After the Program
mode is entered, a delay must be provided to the
device for the automatic bulk write cycle to complete.
This will write all locations in the EEPROM to an all
zeros pattern. The device can then be programmed by
clocking in 16 bits at a time, using S2 as the clock line
and DATA as the data in line. After each 16-bit word is
loaded, a programming delay is required for the internal
program cycle to complete. This delay can take up to
Twc. After every 16-bit word is written to the HCS201,
the HCS201 will signal that the write is complete by
sending out a train of ACK pulses, TACKH high, TACKL
low (if the oscillator was perfectly tuned) on DATA.
These will continue until S2 is dropped. The first pulse’s
width should NOT be used for calibration. 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 DATA. For security reasons, it is not possible to exe-
cute a verify function without first programming the
EEPROM. A Verify operation can only be done
once, immediately following the Program cycle.
Note:
To ensure that the device does not acci-
dentally enter Programming mode, DATA
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
S2
(Clock)
DATA
(Data)
Enter Program
Mode
TPBW TCLKH
TDS
TPS TPH1
TCLKL
TDH
Bit 0 Bit 1 Bit 2 Bit 3
Initiate Data
Polling Here
TCLKL
TWC
Bit 14 Bit 15
T^ACKL T^ACKH
Ack
Ack
T^PHOLD
Ack
Bit 16 Bit 17
TPH2
Write Cycle
Complete Here
Calibration Pulses
Data for Word 1
Repeat for each word (12 times)
Note 1: S0 and S1 button inputs to be held to ground during the entire programming sequence.
FIGURE 6-2:
VERIFY WAVEFORMS
End of Programming Cycle
Beginning of Verify Cycle
DATA
(Data) ^{Bit190 Bit191}
Ack
TWC
S2
(Clock)
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
© 2001 Microchip Technology Inc.
DS41098C-page 13