6.12.5 Data Transmission to MCU

Before beginning data transmission, the FIFO should always be cleared with a reset command (0x0F). Data transmission is initiated with a selected command (see Section 6.13). The MCU then commands the reader to do a continuous write command (0x3D) (see Table 6-7) starting from register 0x1D. Data written into register 0x1D is the TX length byte 1 (upper and middle nibbles), while the following byte in register 0x1E is the TX length byte 2 (lower nibble and broken byte length). The TX byte length determines when the reader sends the EOF byte. After the TX length bytes are written, FIFO data is loaded in register 0x1F with byte storage locations 0 to 11. Data transmission begins automatically after the first byte is written into the FIFO. The loading of TX length bytes and the FIFO can be done with a continuous write command, as the addresses are sequential.

At the start of transmission, the flag B7 (IRQ_TX) is set in the IRQ Status register. If the transmit data is shorter than or equal to 4 bytes, the interrupt is sent only at the end of the transmit operation. If the number of bytes to be transmitted is higher or equal to 5, then the interrupt is generated. This occurs also when the number of bytes in the FIFO reaches 3. The MCU should check the IRQ Status register and FIFO Status register and then load additional data to the FIFO, if needed. At the end of the transmit operation, an interrupt is sent to inform the MCU that the task is complete.