Eilersen MCE2035 - 5 Data Exchange; Profibus-DP Communication Using PPO

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MCE2035: User manual

Version: 2011-05-17, rev.: 0a Page: 8

5) DATA EXCHANGE

5.1 Profibus-DP communication using PPO

Profibus-DP communication with the MCE2035 module uses a so called ’parameter-

process data object’ (PPO) consisting of 26 bytes. This telegram (object) is only used when

transferring data from the slave to the master, since no data are transmitted from the master

to the slave. The structure for this telegram is as follows:

Status(0)

Signal(0)

Status(3)

Signal(3)

0 1 2 3 4 5 6 7 20 21 22 23 24 25

The byte order (MSB/LSB first?) for the individual parts of the telegram is determined by

a jumper. Normally this jumper is set from the factory so that MSB comes first. In the fol-

lowing bit 0 will represent the least significant bit in a register.

LcRegister is a word (two bytes) that constitute a bit register for indication of connected

load cells detected during power on. Hence bit 0-3 will be ON, if the corresponding load

cell (address) was detected during power on. LcRegister is always transferred in 16 bit

unsigned integer format.

LcStatus(X) is a word (two bytes) that constitute a register containing the actual status for

load cell X. LcStatus(X) is always transferred in 16 bit unsigned integer format. During

normal operation this register will be 0, but if an error occurs some bits in the register will

be set resulting in an error code. The meaning of each individual bit in the status register

can be found in the chapter STATUS CODES.

LcSignal(X) is a double word (four bytes) constituting a register containing the actual

weight signal from load cell X. Depending on a jumper LcSignal(X) will be in either 32

bit signed integer format or in IEEE754 floating point format. This jumper is default set

so transfer of LcSignal(X) is done in 32 bit signed integer format. Note that the value is

only valid if the corresponding LcStatus(X) register is 0 indicating no error present. The

scaling of the load cell signal is determined by a DIP-switch as described later.

Since only status and weight for the load cells are transmitted in the telegram, functions

such as status handling, calculation of system weight(s), zeroing and calibration must be

implemented on the Profibus-DP master. Please refer to the chapter DATA PROCESSING

for an explanation on how this typically can be done.