Intermec 1555 Reference Guide

A checksum (CHK) is a calculated value that is used to test data integrity. Table 4-9 
lists the CHK components.

b1

1 bit

Used to indicate a power-on or restart

Receiving a frame with <RestartFlag> set to 1 means that the product has 
just been restarted

Examples:

This flag can be used to check if a desynchronization indicated by the 
FrameNumber bit is due to product/host restart (the FrameNumber 
returned should be set to the same value as the FrameNumber 
received, normally 0)

This flag can also be used to inform the host of a restart in IMC for 
example (any volatile commands may need to be resent)

b0

1 bit

The value of this bit must alternate between 0 and 1 for different 
consecutive frames to detect incorrect frame transmission

Probable causes of incorrect frame transmission are as follows:

Lost low-level ACK

ACK sent too late (timing error, the time-out needs to be changed by the 
corresponding setup command)

Desynchronization due to product/host restart (see <RestartFlag>)

1

0

0

= 04 1st Frame (odd)

1

0

1

= 05  2nd Frame (even)

1

1

0

= 06 Restart. 

Example: 06, 05, 04, 05...