Semi E142.4

SEMI E142.4 defines a bulk item-transfer method for delivering a complete substrate map over SECS-II — sending the entire slot-occupancy result as a single packed binary data block in one transaction, rather than E142.2's approach of reporting individual slot status through discrete status-variable reads. E142.2 works well when a host needs to query a handful of slots or react to per-slot collection events, but reading status variables one at a time, or even as an array of individually-addressed SVIDs, becomes an inefficient way to move an entire carrier's map — 25 slots, or more for larger-format carriers — across the wire every time a full map is needed, which is routinely the case right after a mapping scan completes. E142.4 is the alternative that packages the whole map as one bulk transfer, trading per-slot addressability for a single efficient transaction.

Host needs the complete slot-occupancy map, not just a few slots
E142.2's discrete SVID reads work, but don't scale efficiently to a full carrier
SEMI E142.4 — SECS-II item transfer for substrate mappingEntire map delivered as one packed binary block
Single bulk data transaction for the whole carrier's slot map
One transfer instead of N individual status-variable reads
Standardized binary packing so any compliant host can unpack it
Efficient on the wire, still interoperable across vendors
Host retrieves a full carrier map in one efficient transaction
E142.2 remains available for discrete per-slot queries and events

The reason substrate mapping needed this second SECS-II binding alongside E142.2 is that "read the slot status" and "retrieve the entire map at once" are genuinely different access patterns with different efficiency profiles — a host reacting to a single collection event or checking one slot's status is well served by E142.2's discrete SVID/CEID model, but a host that needs the whole map immediately after a scan completes, which is the common case right before any transport sequence begins, pays an unnecessary transaction-overhead cost doing that as 25 or more separate reads instead of one bulk transfer. E142.4 doesn't replace E142.2; it gives a host the option to request the full map as one packed binary block when that's the access pattern that actually matters, the same kind of efficiency trade E125.2's protobuf encoding makes relative to E125.1's SOAP binding, just applied within SECS-II itself rather than across transports.

25 Transactions vs. One per-slot reads and full-map retrieval are different access patterns E142.2 — one S1F3/S1F4 pair per slot 25 slots = 25 message pairs 25 round trips, 25 protocol overheads E142.4 — one S2F49/S2F50 item-transfer block 01 00 01 00 01 00 00 00 01 01 00 00 01 00 01 01 00 01 ... all 25 slots packed, one block 1 transaction, 1 protocol overhead same information, delivered two very different ways E142.4 doesn't replace E142.2 — it's the fast path for the common case: grab the whole map right after a scan, keep discrete reads for single-slot queries and event reactions

E142.4 is what makes retrieving a complete substrate map an efficient single operation rather than a string of individual slot queries — by defining a bulk item-transfer method that packages the whole carrier's slot-occupancy result as one binary block over SECS-II, it gives a host the fast path for the common case of needing the entire map immediately after a scan, while E142.2's discrete SVID/CEID model remains available for the cases where only a specific slot or event actually matters.

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