Rochester Electronics, LLC AM79865JC-G

The Am79865 PDT converts five-bit encoded parallel symbols into a serial NRZI data stream. Its on-chip PLL derives the bit-rate clock from the local symbol clock. It forms part of AMD's SUPERNET 2 physical-layer chipset with the companion Am79866A receiver and a separate physical-layer controller. This transmitter is not a standalone Ethernet MAC, complete PHY, or receive channel.

• 125-Mbaud serial signaling for 100 Mb/s-class links.
• Five-bit encoded NRZ symbol input and serial NRZI output.
• Integrated transmit PLL requiring an external frequency reference.
• Dedicated electrical loopback path for system test.
• Legacy 20-lead PLCC footprint supported by the original AMD drawing.

AMD documents compliance with ANSI X3T9.5 FDDI, TP-FDDI and 100BASE-TX/FX PHY applications. The PDT takes TDAT[4:0] under LSCLK, serializes the symbols, and offers TX/TY media outputs plus LTX/LTY local loopback outputs. FOTOFF controls optical-transmitter disable in documented designs. The separate Am79866A PDR handles the receive side; its features must not be attributed to this transmitter.

AMD's ordering table maps J to its 20-pin plastic leaded chip carrier drawing PL 020; C denotes 0 to +70 °C commercial temperature. Rochester's exact -G listing specifies PLCC20, 20 pins, tube quantity 48 and lead-free/RoHS supply claims. The local catalog package field is blank. A 20-PLCC register entry exists, but its local JPG is missing. Check the exact Rochester mechanical and finish documentation before assembly.

Assembly checks

• Verify PL 020 dimensions and J-lead seating.
• Confirm pin-one orientation and socket or land pattern.
• Check lot finish, RoHS certificate and solderability.

The AMD 20-pin top-view diagram groups TDAT0-TDAT4 and LSCLK as the local encoded-symbol input, TX/TY as media transmit outputs, LTX/LTY as local loopback outputs, and LPBCK, FOTOFF and TEST as controls. Multiple VCC and GND pins are shown. Use the original numbered drawing, recommended interface circuit and electrical limits for board wiring.

Check DC, timing and absolute-maximum tables for the exact system; 125 MBaud is a signaling rate, not an independent payload-throughput guarantee.

The internal database contains AM79865JC, the original AMD JC transmitter code. It is a reference for engineering comparison, not a qualified drop-in substitute for Rochester's -G supply version; verify finish, compliance, lot and package. The database also contains AM79866AJC, but that device is a receiver, not a transmitter replacement, so no substitution link is presented. Compare the exact pinout, electrical timing and media interface before any change.

AMD authored the June 1996 Rev. D Am79865/Am79866A final data sheet, including the JC ordering code and PL 020 package drawing. AMD's current archive includes related products but an exact original AMD-hosted PDF was not located. Rochester's exact AM79865JC-G listing identifies its present supply code, PLCC20 package, stock, tier prices and lifecycle claim. Request current controlled documentation and certificate traceability before publication.

• Maintenance of legacy FDDI physical-layer boards.
• 100BASE-TX/FX transmitter paths with suitable companion PHY devices.
• TP-FDDI equipment using AMD SUPERNET 2 architecture.
• Repair of qualified commercial-temperature 20-PLCC assemblies.

The local catalog lists 24,143 units at USD 22.88, minimum quantity 11 and no tier ladder. Rochester's exact-code search listing showed 24,138 units and USD 38.15 for 1-24, USD 37.01 for 25-99, USD 35.86 for 100-499, USD 34.72 for 500-999 and USD 33.57 for 1,000 or more. The listing states price and availability are subject to confirmation at ordering, and a direct current checkout quote was not obtained. These values do not reconcile with the local price or stock. No inventory or price fields have been changed; obtain a dated quote and lot/condition evidence first.

Keep this product in manual review and noindex. Restore the local 20-PLCC JPG, reconcile the Rochester stock and tier prices with a dated direct quote, and confirm the -G supply variant, lot provenance and AMD data-sheet limits. Do not publish until all checks pass.