Rochester Electronics, LLC 79865JC

The Am79865 converts five-bit encoded parallel symbols to a serial NRZI data stream. Its transmit phase-locked loop derives the bit-rate clock from the local symbol-clock reference. The complementary Am79866A is a separate receiver, and the Am79C864A is a separate physical-layer controller. The 79865JC is neither a complete Ethernet PHY nor a network controller.

• 125-Mbaud serial signaling for 100-Mb/s-class physical links.
• Five-bit encoded symbol input with NRZI transmit output.
• Integrated transmit PLL using an external reference.
• Electrical loopback provision for qualified system test.
• AMD-defined 20-pin PLCC mechanical outline.

AMD documents use with ANSI X3T9.5 FDDI, TP-FDDI and 100BASE-TX/FX physical layers. TDAT0-TDAT4 carry the encoded parallel symbol under LSCLK; TX/TY provide the transmit media interface and LTX/LTY support local loopback. LPBCK, TEST and FOTOFF are control signals. Receive data recovery belongs to the separate Am79866A, not to this part.

AMD's ordering table defines J as 20-pin plastic leaded chip carrier (PL 020), and C as commercial 0 to +70 degrees C. The product catalog package field is blank. An existing local 20-PLCC registry entry is consistent with AMD's outline, but the associated JPG is missing. Confirm body dimensions, lead condition, pin-one orientation and exact Rochester lot before board assembly.

Assembly checks

• Compare socket or land pattern with AMD PL 020 dimensions.
• Inspect the J-leads and pin-one mark.
• Verify material finish and soldering process for the lot.

The AMD top-view drawing identifies TDAT0-TDAT4 and LSCLK for local symbol input, TX/TY for serial media output, LTX/LTY for local loopback, and LPBCK, FOTOFF and TEST for controls. Multiple VCC and GND terminals are provided. Use the numbered manufacturer drawing rather than this functional summary for wiring.

125 MBaud is a physical signaling rate, not a standalone payload-throughput guarantee. Check the AMD DC, timing and absolute-maximum tables for the actual circuit.

No alternate is linked as a qualified substitute. The AMD Am79865JC and Rochester 79865JC marking relationship requires lot and provenance checks. Am79866A is a receiver, not a transmitter replacement. Confirm pinout, clock and media electrical interface, temperature range and package finish before any substitution.

AMD authored the June 1996 Rev. D Am79865/Am79866A final data sheet, publication 15451, including the JC ordering definition and PL 020 drawing. AMD's current archive also identifies Am79865 as a 100-Mb/s Physical Data Transmitter. Rochester's exact-code listing supplies the present 79865JC commercial listing. Obtain controlled lot documentation for quality approval.

• Maintenance of legacy FDDI physical-layer boards.
• 100BASE-TX/FX transmit paths with separate receive and control devices.
• TP-FDDI equipment based on the AMD SUPERNET 2 architecture.
• Replacement of qualified commercial-temperature 20-PLCC transmitters.

Inspect the exact 79865JC markings, lot and date codes, J-lead condition and source traceability. The local catalog lists 951 units at USD 14.28 with minimum quantity 7 and no tier ladder. DigiKey's Rochester Marketplace exact-code listing also shows 951 units but USD 49.00 at quantity 6, with separate shipping terms. These price and MOQ terms do not reconcile; no catalog commercial field has been changed. Obtain a dated direct quote before publication.

Keep this listing in manual review and noindex until the local 20-PLCC JPG is restored, the empty catalog package field is reconciled with the AMD outline, exact lot provenance is checked, and current stock, minimum quantity and price are confirmed by a dated supplier quote. Do not publish before these checks pass.