HP 8921A Programmer's Manual page 520

Chapter 8, Programming The Call Processing Subsystem
CALL BIT Screen Message Field Descriptions
REGINCR
RSVD
END
OHD
Parity
520
Registration increment field.
12 binary characters required.
Reserved for future use, all bits must be set as indicated.
4 binary characters required.
End indication field.
• Set to 1 to indicate the last word of the overhead message train.
• Set to 0 if not the last word.
1 binary character required.
This field displays the overhead message type.
• A '100' indicates a global action message.
• A '110' indicates this is the first word of the system parameter overhead parameter
message.
• A '111' indicates this is the second word of the system parameter overhead message.
3 binary character required.
Parity field. The contents of the Parity field cannot be set by the user. The Test Set
calculates the parity bits.