MIS — SFP-DD management

MIS, the SFP-DD Management Interface Specification, is published by the SFP-DD MSA for the two-lane SFP-DD form factor. It is not a third management model next to SFF-8472 and CMIS: MIS is a CMIS profile trimmed to two lanes and a single bank, so an SFP-DD module reads like a small QSFP-DD rather than like a big SFP. CodingBox works with MIS 2.0, the current release.

What SFP-DD is

SFP-DD adds a second row of contacts to the SFP cage, doubling the electrical lanes from one to two while keeping backward compatibility with SFP/SFP+/SFP28 modules in the same port. Two lanes at 25G NRZ give 50G, two at 50G PAM4 give 100G; the later SFP-DD112 variant (2 × 56G PAM4) reaches 200G. Mechanical and electrical details: SFP-DD; where it sits among other form factors: Form factors.

Why not SFF-8472

The SFF-8472 map has room for one lane of monitors, one set of flags and a bit-field identity that predates 50G/100G. A two-lane PAM4 module needs per-lane monitors, LOL flags, applications with FEC modes, a power class above SFP+ level 3 and a low-power state — everything CMIS already had. The SFP-DD MSA therefore derived MIS from CMIS and registered two identifiers in SFF-8024:

Identifier	Meaning	Management
1Ah	SFP-DD	MIS
1Fh	SFP-DD with CMIS	CMIS proper

Newer SFP-class modules such as SFP112 skip MIS altogether and use CMIS with identifier 20h (SFP+ or later with CMIS), and DSFP (1Bh) has its own CMIS-derived management. The trend is one model — CMIS — for every new form factor.

Structure

Region	MIS	Notes
Lower page 00h	same layout as CMIS	identifier, revision, module state, flags, module monitors, global controls, media type, application descriptors, password, page select
Upper page 00h	same as CMIS	vendor block, power class, connector, lengths, media technology, page checksum
Page 01h	same as CMIS	advertising: firmware/hardware revisions, wavelength, supported pages, durations
Page 02h	same as CMIS	thresholds
Pages 10h / 11h	2 lanes, bank 0 only	lane control and lane status: Tx disable, data-path states, flags, per-lane Tx/Rx power and bias
VDM, CDB	optional	advertised in page 01h as in CMIS

The module and data-path state machines, application selection through the staged control set, flag semantics and page checksums are those of CMIS. Hosts and tools that speak CMIS can manage an SFP-DD module with lane count and bank count read from the advertising page.

Hardware signals

SFP-DD keeps the SFP low-speed pins where it can — module absent, Tx disable, Tx fault, Rx LOS, rate select — and adds the low-power request and interrupt roles required by a CMIS-style module on the new contact row, as defined in the SFP-DD hardware specification. The two-wire bus is A0h at up to 400 kHz (two-wire interface).

Where you meet it

SFP-DD ports appear on switches and NICs that need 50G/100G in an SFP footprint with backward compatibility for existing SFP28 optics. An SFP28 module in an SFP-DD port is managed via SFF-8472 as usual; only a true SFP-DD module speaks MIS or CMIS. Rate and breakout behaviour follow the CMIS application model — Speed & rate.

In CodingBox

For an SFP-DD module CodingBox selects the MIS/CMIS layout by identifier, decodes the two lanes in DDM, resolves application descriptors through SFF-8024, and edits the vendor block with the page checksum recalculated in the EEPROM editor — the same workflow as for QSFP-DD and OSFP.