Essel Technology RFID A1, User Manual, Page: 57 / 60

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The master must initiate the transmission on the I2C bus by sending a START condition followed by the I2C address of
the slave device with R/W byte set to 0. The second and third byte sent by the master will set up the address index
under which the data will be stored. Starting from the fourth byte the data will be stored under the passed address
value and the memory index will be automatically increased by one each time. When the RFID A1 module recognizes
its I2C address it drives the nBUSY line low to inform the master that it is receiving the data.
5.3.3 Reading from the memory
The master can read from the module in two possible ways presented below in Table 5.4 and Table 5.5.
Table 5.4
Table 5.5
As shown in Table 5.4, to read from a certain address the master first must write the address index by sending a
START condition followed by the I2C address to be written and two bytes representing the index. Later and without
sending a STOP condition the master must send a repeated START signal, this time followed by the I2C address to be
read. Bytes after the I2C read address will be transmitted from the module and will contain memory data starting
from the address index set up by the master at the beginning of the transmission. The index is automatically
increased and stored between transmissions. If the user wants to continue reading data starting from the index
value left since last transmission, he can use the simplified version of the transmission shown in Table 5.5.
Byte number 1 2 3 4 5 5 + n
Value I2C A 0x00 0x00 - 0xFF 0x00 - 0xFF I2C A 0x01 0x00 - 0xFF 0x00 - 0xFF
Type
START + I2C
a Write
Address LSByte Address MSByte
START + I2C
a Read
Data Byte 1 …….. Data Byte n + STOP
Byte number 1 2 2 + n
Value I2C A 0x01 0x00 - 0xFF 0x00 - 0xFF
Type
START + I2C
a Read
Data Byte 1 …….. Data Byte n + STOP