Semi E23

SEMI E23 defines the Cassette-Transfer Parallel I/O Interface, the standard that specifies a simple discrete-signal wiring scheme — individual hardwired lines rather than a structured message protocol — for coordinating cassette hand-off between a wafer-handling tool and an external transport system, such as an operator cart or an early automated guided vehicle. Before SECS-II/HSMS message-based communication (SEMI E4/E37) became the default for equipment-to-host coordination, E23's parallel I/O signals were how a tool told a transport system "ready to receive" or "cassette present" and vice versa — a handful of dedicated wires, each one meaning exactly one thing, rather than a parsed message carrying that same information.

External transport system arrives with a cassette
Operator cart or early AGV, SEMI E23 scope
SEMI E23 parallel I/O handshakeDiscrete hardwired signal lines, not a message protocol
Tool asserts ready-to-receive line
One dedicated wire, one dedicated meaning
Transport asserts cassette-present line
Tool reads the signal directly, no parsing
Cassette hand-off proceeds
Coordinated entirely by discrete signal states

The reason E23's wiring-level approach still shows up in legacy fab equipment is that parallel I/O is mechanically simple and doesn't require any software stack at all on either side of the interface — a signal line is either asserted or it isn't, with no message framing, no session negotiation, and no protocol version to keep in sync between tool and transport system — which made it a practical, low-cost coordination method for an era before every piece of fab equipment carried a networked host connection. This simplicity is also E23's limit: a parallel I/O interface can only ever convey as much information as it has dedicated wires for, so anything requiring structured data — a cassette ID, a lot number, a recipe reference — is fundamentally outside what E23-style signaling can carry, which is exactly the gap SECS-II message-based protocols were built to close as equipment coordination needs grew beyond simple ready/present handshaking.

SEMI E23 — Parallel I/O Signal Wiring each wire carries exactly one fixed meaning Wafer- handling tool Transport system / AGV READY TO RECEIVE (1 wire) CASSETTE PRESENT (1 wire) TRANSFER COMPLETE (1 wire) FAULT (1 wire) No message framing, no protocol version to keep in sync — just discrete asserted / not-asserted wire states structured data like a cassette ID or lot number is outside what this wiring can carry Simple enough to need no software stack — that simplicity is also its hard limit

E23 represents the discrete-signal predecessor to the message-based coordination SEMI E4 (SECS-I) and E37 (HSMS) later standardized, and understanding it matters most when integrating with older installed equipment that still relies on parallel I/O handshaking rather than a networked SECS-II connection.

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