Do IEC 61131-3 languages enforce data type consistency?
. • When using the AT attribute, does the size of a memory location specified by a direct address have to match the size of the variable? The standard is unclear; there are two ways of interpreting the purpose of the direct address. It either specifies a) the actual memory location, in which case the location size and variable type size should match or b) the starting address from which the variable will be located, in which case sizes do not need to match. • When are user specified initialisation values for variables used? User specified initial values apply to non-retentive variables both at “cold restart” and “warm restart”, but they only apply to retentive variables at “cold restart”. On “warm restart” retentive variables have the same values as existed when their resource stopped executing, e.g. due to a power outage. The 61131-3 amendment allows initialisation values defined by the VAR_CONFIG construct to override type specific initial values. Therefore, VAR_CONFIG specified init
