EM4450
EM4550
Selective Read Mode
The Selective Read Mode is used to read other data than that defined between FWR and LWR. To enter Selective Read
Mode, the Transceiver has to send during LIW a Receive mode pattern (RM) to turn the EM4450/4550 in Receive Mode.
Then the Selective Read Mode Command is sent by the transceiver followed by the First and Last addresses to be read.
The FWR and LWR are then replaced by the new addresses and the chip is operating in the same way as the Standard
Read Mode. The control word is not modified by this command, and the next standard read mode operation will work with
original FWR and LWR (Selected area is read once and then the chip returns to Standard Read Mode).
To read words which are Read Protected, a Login command has to be sent by the transceiver prior to the Selective Read
command. The Login command is to be used only once for all subsequent commands requiring a password.
The Selective Read mode command is followed by a single 32-bit word containing the new first and last addresses. Bits 0
to 7 correspond to the First Word Read and bits 8 to 15 correspond to the Last Word Read. Bits 16 to 31 have to be sent
but are not used in the chip. The parities must be sent according to the word organisation as described in fig.7. Note that
bit 31 is transmitted first.
To read the device Identification or the Serial Number, the Selective Read Command allows direct access to the Laser
programmed words. These words can also be addressed in the standard read mode by selecting the addresses
accordingly.
output
input
WORD n LIW
RM Selective RD ADDRESSES
ACK/NAK LIW LIW
FWR
LIW
tpp
Fig. 10
First bit receiv ed
XX XX XX XX XX P3 XX
Addresses Bit Stream Format
XX
XX
XX
XX XX XX XX XX XX
XX P2
LW7 LW6 LW5 LW4 LW3 LW2 LW1 LW0 P1 FW7 FW6 FW5 FW4 FW3 FW2 FW1 FW0 P0 PC7 PC6 PC5 PC4 PC3 PC2 PC1 PC0 "0"
Fig. 11
Reset Command
The Reset Command will return from any mode to the Standard Read Mode. The next word out is the FWR.
output
input
WORD n LIW
RM RESET
ACK/NAK
LIW LIW
FWR
LIW
tpp
tinit
Fig. 12
Login
The Login command is used to access protected memory areas. This command has to be used only once to perform
several password protected commands. The Power-On-Reset sequence and the Reset command will reset the password
entry, and a new Login command has to be received to perform further password protected operations.
Upon reception of a correct password, the EM4450/4550 will respond with an acknowledge pattern (ACK) and then
continue in Standard Read Mode. If the Login is correct then password protected operations are allowed. If the password is
incorrect, a NAK pattern is issued and password protected operations will not be possible (refer to Write Word for password
data structure).
output
input
WORD n LIW
RM LOGIN
ACK/NAK LIW LIW
FWR
LIW
PASSWORD
tpp
Fig. 13
7
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