How does SECSC work?
SECSC functions provide a interface at the HSMS or the SECS-I "transaction level".
To send a message to the host and receive a reply, only one function
call is required. SECSC takes care of putting together the message header, breaking long messages
up into blocks, sending the message, and waiting for and receiving the reply.
Whether the equipment is the originator or interpreter of a transaction, SECSC coordinates the
primary and secondary message pairs. The program deals with the stream and function codes and
the body of the message. SECSC provides the equipment controller program with a wealth of features
to simplify the processing of SECS-I/HSMS transactions. After a message has been received, data items
formatted according to the SECS-II standard can be automatically picked out of the body and placed
directly into C program variables known to the application program. SECS-II messages can be formatted
from C program variables and sent. SECSC handles all the data translation and alignment requirements.
SECSC, besides sending and receiving the message bytes, checking checksums, timing the arrival of bytes
and so on, also merges multiblock messages into single data bodies for processing.
It can send some classes of error messages automatically. SECSC takes completed transactions,
looks them up in a table of streams and functions (which you have provided) and dispatches to message
handlers that process them. It can also perform automatic message formatting and unformatting for
simple message structures.
SECSC Modules
The SECSC package contains two sets of functions for formatting and unformatting SECS-II messages.
- The MSGBDY module contains body formatting functions that act on an entire message body at once.
- The MSGSTM module contains stream formatting functions,
which are used to format or unformat one item at a time.
Either set of functions can be used with SECSC or as stand-alone functions for special applications.
SECSC uses the body formatting functions to perform automatic formatting.
The SECSC package contains the:
- MSGITEM module, a set of functions for storing and formatting SECS messages and message items,
using a linked list of item structures;
- ASCCVT module, for converting SECS-II data items to and from ASCII representations;
- MSGCVT module, for converting SECS-II data items from one SECS-II data type to another;
- COMPVALS module, for comparing SECS-II data items; and
- LIMITVAL module, containing limit definitions for each SECS-II item type.
SECSC-I requires an RS-232-C serial port for sending and receiving bytes and a timer.
HSMS uses a TCP/IP connection.
Integrating SECSC into a system is dependent on the system environment (hardware and operating system).
SECSC is designed to work, without modification, in most stand-alone and multiprocessing programming
systems. With either system, SECS message I/O will take place in the background allowing the program
to perform other tasks concurrently. FabMation also sells a product called
GEMLib, which works with SECSC to provide a complete
package for supporting the GEM standard on your equipment.
Features of SECSC
- Full HSMS and SECS-I protocol implementation plus SECS-II error handling features.
- Extensive error detection and reporting capabilities with automatic error message generation.
- Powerful transaction-level interface.
- Multiple, open transactions supported.
- Automatic multiblock buffering.
- Conversation timing capability.
- Programming system independence.
- SECS messages sent and received in the background.
- C source code with options for customization.
- Automatic formatting and unformatting of SECS-II item data.
- Automatic dispatch to transaction handlers.
- Automatic memory allocation and management.
- Conversation protocol support for sequencing transactions.
- Complete error handling and recovery strategy.
Features of Body Formatting Functions (MSGBDY Module)
- Formats and unformats entire message bodies.
- Simple but powerful specification language to define the formatting and unformatting actions.
- Specify lists of duplicate items and items with unknown formats.
- Alignment configurations can handle a wide variety of compiler and machine requirements.
- Features of Stream Formatting Functions (MSGSTM Module):
- Data is moved one item at a time.
- Complete program control over formatting and unformatting.
- Low memory requirements.
- Automatic data alignment and byte reversal.
Features of Message Item Storage (MSGITEM Module)
- A single struct is used to represent any SECS-II item type.
- Consistent treatment of all SECS-II item types.
- Item lists can represent any SECS-II message regardless of complexity.
- Formatting and unformatting functions permit simple translation of item lists to and from SECS-II messages.
- Features of ASCII Conversion (ASCCVT Module):
- Convert any SECS-II data atom (except 8-byte integers) to or from an ASCII representation.
- Convert SECS-II data format codes to and from an ASCII representation.
- Convert SECS-II item vectors to or from an ASCII representation.
Features of Message Data Conversion (MSGCVT Module)
- Convert SECS-II data atoms from one type to another.
- Allow received messages to use any item type, but convert to a convenient internal type.
- Supports conversion from ASCII string representation to and from other types.
- Features of Message Item Comparison (COMPVALS and LIMITVAL Modules):
- Determine relationship of two SECS-II items (equal, less, or greater) when data type is unknown until run time.
- Handy set of global variables containing absolute limits for each SECS-II item type.
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