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SAB 82532/SAF 82532
Basic Functional Principles
Semiconductor Group
37
07.96
2
Basic Functional Principles
2.1
The ESCC2 distinguishes itself from other communication controllers by its advanced
characteristics. The most important are:
– Support of HDLC, SDLC, BISYNC/MONOSYNC and Asynchronous protocols
– Support of layer-2 functions (HDLC mode)
In addition to those bit-oriented functions commonly supported by HDLC controllers,
such as bit stuffing, CRC check, flag and address recognition, the ESCC2 provides a
high degree of procedural support.
– In a special operating mode (auto-mode), the ESCC2 processes the information
transfer and the procedure handshaking (I- and S-frames of HDLC protocol)
autonomously. The only restriction is that the window size (= number of outstanding
unacknowledged frames) is limited to 1, which is sufficient for many applications. The
communication procedures are mainly processed between the communication
controllers and not between the attached processors. Thus the dynamic load on the
CPU and the software expense is greatly reduced.
– The CPU is informed about the status of the procedure and has mainly to manage the
receive and transmit data. In order to maintain cost effectiveness and flexibility, the
handling of unnumbered (U) frames, and special functions such as error recovery in
case of protocol errors, are not implemented in hardware and must be done by the
user’s software.
– Extended support of different link configurations
Besides the point-to-point configurations, the ESCC2 allows the implementation of
point-to-multipoint or multi-master configurations without additional hardware or
software expense.
In point-to-multipoint configurations, the ESCC2 can be used as a master or as a
slave station. Even when working as slave station, the ESCC2 can initiate the
transmission of data at any time. An internal function block provides means of idle and
collision detection and collision resolution, which are necessary if several stations
start transmitting simultaneously. Thus, a multi-master configuration is also possible.
General