HCS412I MICROCHIP [Microchip Technology], HCS412I Datasheet - Page 34

• Manufacturer Part Number: HCS412I
• Description: KEELOQ Code Hopping Encoder and Transponder
• Manufacturer: MICROCHIP [Microchip Technology]

HCS412
7.0
The HCS412 requires some parameters programmed
into the device 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 is initiated by forcing the DATA line high,
after the S2 line has been held high for the appropriate
length of time line (Table 7-1 and Figure 7-2).
A delay is required after entering Program mode while
the automatic bulk erase cycle completes. The bulk
erase writes all EEPROM locations to zeros.
The device is then programmed by clocking in the
EEPROM memory map (Least Significant bit first) 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.
FIGURE 7-1:
FIGURE 7-2:
FIGURE 7-3:
DS41099C-page 34
(Clock)
(Clock)
Note 1: S0 and S1 button inputs to be held to ground during the entire programming sequence.
(Data)
DATA
(Data)
DATA
S2
S2
Note: If a Verify operation is to be done, then it must immediately follow the Program cycle.
End of Programming Cycle
Production
Programmer
Manufacturer’s
PROGRAMMING THE HCS412
Enter Program
Bit190
T
PS
Code
Mode
T
Bit191
PH
1
T
PH
CREATION AND STORAGE OF CRYPT KEY DURING PRODUCTION
PROGRAMMING WAVEFORMS
VERIFY WAVEFORMS
2
T
T
WC
PBW
T
Serial Number
Bit 0
CLKH
Transmitter
Ack
T
Generation
CLKL
Algorithm
Bit 1
Key
T
Data for Word 0
Bit 2
DS
Bit 0
(KEY1_0)
Beginning of Verify Cycle
T
Bit 3
DH
Bit 1 Bit 2
T
Preliminary
Repeat for each word (18 times total)
DV
Bit 14
Data from Word 0
Bit 3
Bit 15
Crypt
Key
Write Cycle
Complete Here
T
CLKL
The HCS412 will signal a ‘write complete’ after writing
each 16-bit word by sending out a series of ACK pulses
T
tinue until S2 is dropped.
Programming verification is allowed only once, after the
programming cycle (Figure 7-3), by reading back the
EEPROM memory map. Reading is done by clocking
the S2 line and reading the data bits on DATA, again
Least Significant bit first. For security reasons, it is not
possible to execute a Verify function without first pro-
gramming the EEPROM.
ACKH
T
Note:
WC
Initiate Data
Polling Here
Bit 14
high, T
Ack
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.
Bit 15
ACKL
HCS412
Calibration Pulses
low on DATA. The ACK pulses con-
Ack
Bit 16 Bit 17
2002 Microchip Technology Inc.
EEPROM Array
Serial Number
Ack
Crypt Key
Sync Counter
.
.
.
Bit190 Bit191
Bit 16
Data for Word 1
(KEY1_1)
Bit 17