Sim Crc Block; Figure 25-15 Cyclic Redundancy Check Circuit Diagram - Motorola DragonBall MC9328MX1 Reference Manual

25.4.6 SIM CRC Block

The SIM provides an 16-bit CRC generator/checker. The block is provided for use with T = 1 SmartCards
that support CRC. This block is enabled through the CRC enable (CRCEN) bit in the CNTL register. This
block performs a polynomial based check on all received or transmitted characters. A description of the
polynomial is shown in Figure 25-15 on page 25-17.
Input/Output
Data Stream
next bit
Output TRANSMIT
Data Stream
CRC16 Transmitted MSB
first after final data byte
Figure 25-15. Cyclic Redundancy Check Circuit Diagram
At the end of the reception of a block of characters, the residual from the CRC calculation is compared to
0x1D0F. If it matches correctly, the CRCOK bit is set in the RCV_STAT register. During transmission, the
CRC block updates the current value of each character in the CRC residual. When the
XMT_EN_LRC_CRC bit in the CNTL register is set, the CRC value is automatically inverted and sent by
the SIM transmitter as the final two characters when the transmit FIFO empties.
MOTOROLA
• Update every bit time
• Reset to 1s at SOP
16
0
RECEIVE
Good CRC
SmartCard Interface Module (SIM)
Generated Polynomial
0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 1
0
1
MUX
16
16
0 0
Equal?
Yes No
SIM Port Controller
16
Expected Residual
0 1 1 1 0 1 0 0 0 1 1 1 1
16
Bad CRC
25-17