To Next Page

To Previous Page

5. Initial Programming

229

5. Initial Programming

The main goal of this chapter is to help in the programming and configuration of Nexto Series CPUs

so that the user will be able to take the first steps before starting a controller programming.

Nexto Series CPU uses the standard IEC 61131-3 for language programming, which are: IL, ST, LD,

SFC and FBD, and besides these, an extra language, CFC. These languages can be separated in text

and graphic. IL and ST are text languages and are similar to Assembly and C, respectively. LD, SFC,

FBD and CFC are graphic languages. LD uses the relay block representation and it is similar to relay

diagrams. SFC uses the sequence diagram representation, allowing an easy way to see the event

sequence. FBD and CFC use a group of function blocks, allowing a clear vision of the functions

executed by each action.

The programming is made through the MasterTool IEC XE (IDE) development interface. The

MasterTool IEC XE allows the use of the six languages in the same project, so the user can apply the

best features offered by each language, resulting in more efficient applications development, for easy

documentation and future maintenance.

For further information regarding programming, see User Manual MasterTool IEC XE - MU299609,

Programming Manual MasterTool IEC XE - MU399609 or IEC 61131-3 standard.

Memory Organization and Access

Nexto Series uses an innovative memory organization and access feature called big-endian, where the

most significant byte is stored first and will always be the smallest address (e.g. %QB0 will always

be more significant than %QB1, as in Table 5-1, where, for CPUNEXTO string, the letter U is byte 0

and the letter O is the byte 7).

Besides this, the memory access must be done carefully as the variables with higher number of bits

(WORD, DWORD, LONG), use as index the most significant byte, in other words, the %QD4 will

always have as most significant byte the %QB4. Therefore it will not be necessary to make calculus

to discover which DWORD correspond to defined bytes. The Table 5-1, shows little and big endian

organization.

MSB  Little-endian (Traditional)  LSB

BYTE

%QB7

%QB6

%QB5

%QB4

%QB3

%QB2

%QB1

%QB0

WORD

%QW3

%QW2

%QW1

%QW0

DWORD

%QD1

%QD0

CPUN

EXTO

LWORD

%QL0

CPUNEXTO

HSB <– Big-endian (NEXTO) –> LSB