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HCS515

KEELOQ Code Hopping Decoder

Microchip Technology 

HCS515

4.2.5 READ BYTE/S FROM USER EEPROM

4.2.6 WRITE BYTE/S TO USER EEPROM

The read command (Figure 4-4) is used to read bytes

from the user EEPROM. The offset in the user

EEPROM is specified by the address byte which is

truncated to seven bits (C to D). After the address, a

dummy byte must be clocked in (D to E). The EEPROM

data byte is clocked out on the next rising edge of the

clock line with the least significant bit first (E to F).

Sequential reads are possible by repeating sequence E

to F within 1 ms after the falling edge of the previous

byte’s Most Significant Bit (MSB) bit. During the

sequential read, the address value will wrap after 128

bytes. The decoder will terminate the read command if

no clock pulses are received for a period longer than

1.2 ms.

The write command (Figure 4-5) is used to write a loca-

tion in the user EEPROM. The address byte is trun-

cated to seven bits (C to D). The data is clocked in least

significant bit first. The clock line must be asserted to

initiate the write. Sequential writes of bytes are possible

by clocking in the byte and then asserting the clock line

(D – F). The decoder will terminate the write command

if no clock pulses are received for a period longer than

1.2 ms After a successful write sequence the decoder

will acknowledge by taking the data line high and keep-

ing it high until the clock line goes low.

4.2.7 ERASE ALL

The erase all command (Figure 4-6) erases all the

transmitters in the decoder. After the command and two

dummy bytes are clocked in, the clock line must be

asserted to activate the command. After a successful

completion of an erase all command, the data line is

asserted until the clock line goes low.

FIGURE 4-4: READ BYTES FROM USER EEPROM

TRD

TRD

CLK

µC DATA

LSB

MSB LSB

MSB LSB

MSB

Decoder DATA

Start Command

A

B

Command Byte

C

Address Byte

D

Dummy Byte

LSB

MSB

Data Byte

E

F

FIGURE 4-5: WRITE BYTES TO USER EEPROM

CLK

µC DATA

LSB

MSB LSB

MSB LSB

TWR

TACK

TRESP

MSB

TACK2

Decoder DATA

Start Command

A

B

Command Byte

C

FIGURE 4-6: ERASE ALL

Address Byte

Data Byte

D

E

TERA

CLK

µC DATA

LSB

MSB LSB

MSB LSB

MSB

Decoder DATA

Start Command

A

B

Command Byte

Subcommand Byte

Dummy Byte

C

D

E

Acknowledge

F

TACK

TRESP

TACK2

Acknowledge

F

DS40183A-page 10

Preliminary

© 1998 Microchip Technology Inc.

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