Command Definition/General
Applicable release versions: R83, AP
Category General (155)
Description describes a system error. A frame containing data, either workspace or file system data was not properly linked to a previous frame of data. Instead, this backward "pointer" was zero. The system was traversing data backward and "ran off" the beginning of the data.

Each frame of data has both forward and backward links. If the frame has a zero backward link it is usually the first frame detailing some information or document, etc. Any frame with a backward link can be "chased" through the backward chain of frames to find the first frame (beginning of the data).

When at tcl, use "dump" with the "lu" options to travel backward through links. When in the system debugger use the "l" command to see the links of a frame and <ctrl>+p to travel backward one link.
Syntax Backward Link Zero ; reg = {number} abort @ {abs mode}

I ut.go.debug:07E

 see, displayed: 

!l740220  740220    0 :  740221     740219 : 0  =

at the = sign a <ctrl>+p will display the link fields for the previous 
frame 740219 and a <ctrl>+n will display the link fields for the next 
frame 740221.
Related tcl.dump