User Manual
Chapter 12
GFK-1742F
Jan 2020
Local Logic Language Syntax
300
12.7
Local Logic Runtime Errors
12.7.1
Overflow Status
Some arithmetic operations may have results that cannot be correctly represented as a
signed 32-bit value. An example is shown in the following code segment.
In the first line, P001 is loaded with 2,147,483,647, the largest value that can be represented
as a 32 bit signed two’s
-complement value. In the second line, one is added to that value.
The total, represented in hexadecimal, is 16#8000_0000. This value, interpreted as a 32-bit
signed two’s complement number represents the negative value –
2,147,483,648, not the
positive value 2,147,483,648! In many situations, this result would be unexpected and have
undesirable effects in subsequent program statements.
Three variables are available to the Local Logic program to detect overflows. The Overflow
variable is a read-write Boolean variable available only to the local logic program (refer to
Chapter 13, Se
ction on “Local Logic System Variables”). When an overflow e
rror occurs, and
the Overflow variable is not cleared before the end of the Local Logic sweep, the DSM’s
Module Status Code %AI word (local logic variable Module_Status_Code) is set. The error
code indicates the type of overflow and the Module Error Present %I bit (local logic variable
Module_Error_Present) is set. The Module Status Code %AI word and the Module Error
Present %I bit are not set until the current Local Logic sweep has finished executing. In
contrast, the Overflow variable is set immediately following an instruction which causes an
overflow. The Local Logic program may clear the Overflow variable by assigning it a value of
zero. The Module Status Code must be cleared by the host controller by setting the
module’s Clear Error %Q bit.
Overflow and computation errors are Status Only errors with two exceptions. A divide by
zero or divide overflow (the quotient cannot be represented in 32 bits) are Stop Fast errors.
In the case of status only errors, Local Logic processing and path generation continue
normally. A stop fast error will cause Local Logic processing to be aborted before proceeding
to the next instruction, and any motion will be aborted by setting the servo velocity
command to zero. Note: Clearing the Overflow variable has no effect on Stop Fast errors.
Refer to Table 63 for a listing of all Runtime Local Logic error codes.
Divide By Zero
The Logic Engine flags Divide By Zero operations as a Fast Stop Error, since the result of the
operation is undefined. Local Logic execution and servo motion is halted. An error code
16#2093 is reported in the module status code and 16#2x9A in the Per-Axis error codes if
the drives were enabled.