Technical data

Using the services for the actual data transfer
The data to be transmitted (max. 242 bytes "net data") and the received
data (also max. 242 bytes) should be stored in a data block; it can,
however, also be stored in the flag area.
The data to be transmitted and received is always preceded by an 8 byte
header containing control and status information for the layer 2 firmware.
When calculating the memory required for transmitted and received data
(parameters QLAE or ZLAE when calling a handling block) these 8 bytes
must be taken into account. The data including the header form the general
interface for calling the services, known as the "job buffer". The action is
triggered by an application program via the job buffer. The job buffers are
transferred to the interface module via the dual-port RAM using the
standard handling blocks. The job buffer itself is used to transfer the
parameters for correct execution of the service on the interface module. Job
buffers must always be in the data block area or in the extended data block
area and are restricted to a maximum length of 250 bytes. Each job buffer
consists of a header and a data .
Fig. 8.1 illustrates the basic structure of a job buffer. The description of the
header is in the key to the figure. The user must create the job buffer for
specific services.
Free Layer 2 Communication B8976060/02
Volume 1 8 - 4