Functional description
5
gas-lab
Q1
Page 91
5.6.2.2
Protocol-specific facts: RK512 / 3964R
The gateway functionality of the
gas-net
Q1 supports the protocol consisting of
3964R (data link layer) and RK512 (data presentation).
Look up the settings of the protocol parameters in exactly this form in the
manuals of the programmable controller and adjust them in the communications
processor procedure.
The implementation of the RK512 protocol in the
gas-net
device is restricted to
the data transmission between data blocks. The smallest information unit is a
data word
. Such a data word has a length of 16 bits and may contain, for
instance, several messages, a status overview in the form of a bit string, or a
binary measurement.
The structure of the management of these data words is rather simple; there are
up to 256 larger units, called
data blocks
, each of which may contain up to 256
data words. Data blocks and data words are numbered consecutively from 0 to
255, with the numbers serving as addresses.
A single data word is clearly defined by exactly three details:
the address of the data block (0..255)
the address of the data word (0..255)
the content of the data word
The addresses to be assigned to the host data in the
gas-net
parameterisation
therefore consist of a data block/data word (DB/DW) pair. Data block 0 is usually
used for intrasystem host variables. This is why you should use data block 0
neither for exporting values towards the host nor for importing host values.
In special cases it may happen that the host only masters the subordinate
3964R protocol layer. This means that the following restriction applies: As no
DB/DW information is transmitted on the 3964R protocol level, all data to be
exported or imported must be arranged as a string. The number of dates is thus
limited to 64 data words per transmission. This is why in the GW-GNET+
interface (
Data exchange
module) the positions for import and export values are
not indicated in the DB/DW form but as serial register numbers.