IDL 101
COMMUNICATION
72
HB_IDL101_E_V222.doc
Gantner Instruments Test & Measurement GmbH
10.3.3. Instruction Set
Layer 2-adaption in the PROFIBUS-protocol:
With PROFIBUS every bus user has so-called "service access points" (SAPs), via which he can exchange data with the
communication partners. With the
Datalogger IDL 101 the SAPs are used for identifying (addressing) the various data
and commands of the data logger. By specifying the DSAP-number (DSAP: Destination SAP) in the data field of the
request telegram the data logger can be informed as to which data shall be transmitted or which function the data
logger shall carry out. The data logger can also be informed as to which own SAP (SSAP: Source SAP) the data are to
be returned to.
Request/Response telegram (example SD2-telegram):
SD2
LE
ReqDataUnit
DA
DSAP
LEr
SD2
SA
FC
FCS
ED
Data
Data
Data
Data
DSAP
SSAP
DSAP SSAP
SSAP
= 0
= 0
> 0
= 0
= 0
> 0
> 0
> 0
ResDataUnit
A DSAP- or SSAP-entry respectively is identified by setting the highest bit in the address byte of Destination-Address
(DA) or Source-Address (SA) respectively. The entry itself is carried out in the first, resp. the second position in the
ReqDataUnit data field.
The DSAP- and SSAP-entries in the request telegram also appear in the response telegram, where DA, SA, DSAP and
SSAP in the response telegram correspond to SA, DA, SSAP and DSAP in the request telegram!
If no storage expansion is carried out in the request telegram, the orders are carried out via the Default-SAP. The
Default-SAP has the number 0. It does not have to be indicated separately in the telegram.
DSAP and SSAP entries are only possible with telegrams with data field (SD2 and SD3 telegrams).