hcs500 Microchip Technology Inc., hcs500 Datasheet - Page 11

• Manufacturer Part Number: hcs500
• Description: Keeloq Code Hopping Decoder
• Manufacturer: Microchip Technology Inc.

4.2.5
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.
FIGURE 4-4:
FIGURE 4-5:
2002 Microchip Technology Inc.
Decoder
Decoder
C DATA
C DATA
DATA
CLK
DATA
CLK
A
A
READ BYTE/S FROM USER
EEPROM
Start Command
Start Command
READ BYTES FROM USER EEPROM
WRITE BYTES TO USER EEPROM
B
B
LSB
LSB
Command Byte
Command Byte
MSB
MSB
C
LSB
C
LSB
Address Byte
Address Byte
MSB
MSB
4.2.6
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 keeping it high until the clock line
goes low.
D
D
LSB
LSB
Data Byte
WRITE BYTE/S TO USER EEPROM
Dummy Byte
MSB
MSB
T
WR
T
RD
E
E
LSB
Acknowledge
T
HCS500
ACK
Data Byte
DS40153C-page 11
MSB
T
RD
T
RESP
F
T
ACK
F
2