HCS412 Datasheet, PDF (24/44 Pages) Microchip Technology – KEELOQ Code Hopping Encoder and Transponder

HCS412
4.3.4 BULK ERASE
A Bulk Erase resets the HCS412’s memory map to all
zeros. The transponder reader selects the appropriate
device through anticollision, as need be, issues the
PROGRAM command followed by the device’s 28-bit
transport code, then resets the device by removing the
field for 100 ms.
Resetting the device after the PROGRAM command
results in a bulk erase, resetting the EEPROM memory
map to all zeros. This is important to remember as the
reader must now communicate to the device using the
communication options resulting from a zero’d configu-
ration word - baud rates, modulation format, etc.
(Table 5-1).
FIGURE 4-7: BULK ERASE
Activate
Field ^ACK
Delay to
Command
Command
Delay to
TCODE
28-bit
Transport
Code
Delay
Device Reset
TPU
TATO
TOTD
6ms
100ms
ACK
2 LFTE
Start
Communication from reader to HCS412
Communication from HCS412 to reader
Program
Command
2 LFTE
Start
28-bit
Transport
Code
4.3.5 PROGRAM
Inductive programming a HCS412 begins with a bulk
erase sequence (Section 4.3.4), followed by issuing
the PROGRAM command and the desired EEPROM
memory map’s 18x16-bit words (Section 5.0). The
HCS412 will send a write Acknowledge after each word
has been successfully written, indicating the device is
ready to receive the next 16-bit word.
After a complete 18 word memory map has been
received and written, the HCS412 PPM modulates 18
bursts of 16-bit words on the LC pins for write verifica-
tion. Each word follows the standard HCS412 response
format with a leading 1LFTE low START pulse and ‘01b’
preamble (Figure 4-10).
Since the bulk erase resets the configuration options to
all zeros, the oscillator tuning value will also be cleared.
The correct tuning value is required when the program-
ming sequence sends the new configuration word. The
value may either be obtained by reading the configura-
tion word prior to bulk erase to extract the value or by
determining TE from the field Acknowledge sequence
and calculating the tuning value appropriately
(Section 4.2.1).
TABLE 4-6: PROGRAM COMMANDS
Command
Description
Expected data In
Response
01000 Program HCS412 EEPROM
Transport code (28 bits); Com- Write Acknowledge pulse after
plete memory map: 18 x 16-bit each 16-bit word, 288 bits trans-
words (288 bits)
mitted in 18 bursts of 16-bit words
FIGURE 4-8: PROGRAM SEQUENCE - FIRST WORD
Activate
Field ^ACK
Delay to
Command
Command
Delay to
TCODE
28-bit
Transport
Code
Delay to
Data
Delay before Write
16 bits Data _{Write ACK ACK}
TPU
TATO
TOTD
TTTD
TWR
ACK
2 LFTE
Start
Communication from reader to HCS412
Communication from HCS412 to reader
Program
Command
2 LFTE
Start
28-bit
Transport
Code
2 LFTE
Start
16
Data Bits
Write Delay ACK
Repeat 18 times for programming
DS41099C-page 24
Preliminary
© 2002 Microchip Technology Inc.