B.2 Reflected bits

07.103GPPTerminal Equipment to Mobile Station (TE-MS) multiplexer protocolTS

In the example the bits where shown as they was sent on the serial line, this is however not they way the application sees the octets, it will see MSB first and LSB last, so before calculating the FCS the octets bit order must be reversed.

BOFC

DLC

Ctrl

FCS

EOFC

0xF9

0x07

0x3F

0xF9

11111001

00000111

00111111

To be calculated

11111001

1 Reverse all bit in octets

2 Calculate FCS

3 Reverse all bits in FCS

4 Send the reversed FCS

Fortunately there is an easier way of doing the reversing of the bits, when implementing the CRC calculation using table lookup the table can be reversed.