Motorola DragonBall MC9328MX1 Reference Manual page 725

the protocol is initiated with a block transfer from the SIM. To send the response or the first block, the
following steps must be performed:
1. Set the desired transmit FIFO threshold level by writing the TDT bits in the
XMT_THRESHOLD register.
2. Write the characters to be sent as response (maximum 16) to the transmit FIFO in the
XMT_BUF register.
3. Clear all transmit interrupt flags in the XMT_STAT register by writing 1 to them.
4. Enable the transmit interrupts desired by clearing the mask bits in the INT_MASK register.
When sending more than 16 characters, use the TDTF interrupt to signify when to write
more characters to the transmit FIFO. This results in the most efficient transfer time to the
SmartCard.
5. Enable the transmission of the error checking characters (LRC or CRC) by setting the
XMT_EN_LRC_CRC bit in the CNTL register.
When the card supports PPS, the software may not be allowed to send the
LRC or CRC information until the PPS exchange is completed. If so, do
not set the XMT_EN_LRC_CRC bit during the PPS exchange.
6. Enable the transmitter by setting the XMT_EN bit in the ENABLE register.
At this point, the SIM transmits the characters in the transmit FIFO. When sending more than 16
characters, the transmit threshold interrupt is set when the threshold number of characters are remaining in
the FIFO. The software can then write an additional number of characters to be sent without interrupting
transmission to the SmartCard.
When the transmission is complete, the SIM is completely configured for standard operation with the T = 1
SmartCard. The software can continue to service RDRF interrupts for received characters, and TDTF
interrupts for transmitted characters.
MOTOROLA
Suggested Programming Models for Specific SmartCards
NOTE:
SmartCard Interface Module (SIM) 25-55