Issue link: https://iconnect007.uberflip.com/i/1091269
42 PCB007 MAGAZINE I MARCH 2019 ment communications standard (SECS) [6] . SECS define parts of all seven ISO OSI communications lay- ers. SECS/GEM standardizes two- way communication within a net- work or serial cable that connect equipment and is independent of any particular programming or computer operating system. One HP Journal [7] explained SECS this way. "SECS I incorporates the use of RS-232-C cabling and pin defini- tions and a relatively simple line protocol. SECS II defines messag- es to request and sends status in- formation, transfers recipe data, reports alarm conditions, sends remote equipment control com- mands, and handles material trans- fer. SECS I uses a simple ENQ-ACK handshake across an RS232-C line with checksums at the end of each message. SECS I also defines time- out intervals between handshake responses, individual message characters, and message responses. Message headers are defined in SECS I to in- clude equipment identifiers, message identifi- ers, message block numbers, and other system information. SECS II define message types, format, con- tent, and directions. SECS streams are groups of messages assigned to a general set of equip- ment functionality. Within each stream, the in- dividual messages are assigned function num- bers. For example, SECS stream 1 function 5 (abbreviated S1 F5) is a formatted equipment status request, and stream 1 function 6 is the reply with the status information. Similar- ly, stream 7 function 5 is used to request the transfer of a process recipe and stream 7 func- tion 6 is used to transfer the recipe. SECS II also defines whether a reply is required or not, the message content and format (including data item definition headers), and whether a message may be used from equipment-to-host and/or host-to-equipment." A major limitation of the SECS standard is that it defines messages and their content only; it does not define how the messages are used to- gether to perform a function. Equipment man- ufacturers are left to decide what messages to use to perform functions that were performed manually before. This, of course, makes it diffi- cult to develop translators for external systems to communicate with such equipment. Figure 4 shows more details of the SECS II/GEM stan- dard built on the OSI seven-level communica- tion model [5] . Open Manufacturing Language (OML) OML provides an intelligent IoT connectivity platform for all PCB assembly production ma- chines and processes, whether automated or manual while enabling support—such as plan- ning, supply chain, and quality management— and corporate systems, such as MES, ERP, and PLM. The standard is the proprietary develop- Figure 4: SEMI's SECSII/GEM communication standard documents ma- chine connectivity and controls/recipes [7] .