HCS362-I Datasheet, PDF (20/38 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

HCS362
5.0 PROGRAMMING THE HCS362
When using the HCS362 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 288 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
(Table 5-1 and Figure 5-1). 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 includ-
ing the OSC calibration bits.
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 pro-
gramming delay is required for the internal program
cycle to complete. This delay can take up to Twc. At the
end of the programming cycle, the device can be veri-
fied (Figure 5-2) by reading back the EEPROM. Read-
ing is done by clocking the S2 line and reading the data
bits on DATA. For security reasons, it is not possible to
execute 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
accidentally enter Programming mode,
PWM should never be pulled high by
the circuit connected to it. Special care
should be taken when driving PNP RF
transistors.
FIGURE 5-1:
PROGRAMMING WAVEFORMS
Enter Program
Mode
S2 (S3)
(Clock)
DATA
(Data)
TPS TPH1
TPBW
TCLKH
TDS
TCLKL
TDH
Bit 0 Bit 1 Bit 2 Bit 3
Bit 14 Bit 15
TWC
TPH2
Data for Word 0 (KEY_0)
Repeat for each word (18 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.
Bit 16 Bit 17
Data for Word 1
FIGURE 5-2:
VERIFY WAVEFORMS
End of Programming Cycle Beginning of Verify Cycle
DATA
(Data)
Bit286 Bit287
S2 (S3)
(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.
Bit286 Bit287
DS40189D-page 20
Preliminary
© 2002 Microchip Technology Inc.