NXP Semiconductors KMC68EN302AG25BT

Overview

KMC68EN302AG25BT from Freescale is a 144-pin TQFP integrated multiprotocol processor with embedded 10 Mbps IEEE 802.3 Ethernet controller, DRAM controller supporting up to 8 MB per bank, and three SCC serial channels - designed for low-end bridges, ISDN-to-Ethernet routers, and remote LAN access points.

For engineers reviewing the KMC68EN302AG25BT datasheet, KMC68EN302AG25BT pinout, KMC68EN302AG25BT application, or KMC68EN302AG25BT equivalent, key selection considerations include its 25 MHz operation, 5 V supply, IEEE 1149.1 JTAG compliance, dual 128-byte Ethernet FIFOs, and glueless DRAM interface with programmable refresh and CAS/RAS control.

Technical Context

The KMC68EN302AG25BT integrates a MC68000-compatible microcoded core with an IEEE 802.3-compliant Ethernet protocol core, two dedicated DMA channels (Tx/Rx), and a dual-port RAM-based descriptor engine - enabling collision handling and frame buffering without CPU bus overhead. Its DRAM controller supports two banks, 80 ns DRAM at 25 MHz zero-wait-state operation, and address multiplexing for external bus masters.

The module bus controller mediates between the internal 68000 bus and external peripherals, handles interrupts from Ethernet and DRAM blocks, and coordinates bus arbitration among internal and external masters. The Ethernet controller implements full-duplex (20 Mbps) operation, 64-entry CAM with hash, heartbeat monitoring, and loopback test mode - all accessible via the standard 68302 programming model.

Key Specifications

Pinout & Package

Package: 144-lead Low-Profile Thin Quad Flat Pack (TQFP), 20 × 20 mm, 0.5 mm pitch, RoHS-compliant lead finish.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar integrated multiprotocol processor applications.

Compared with MC68EN302PV25, KMC68EN302AG25BT offers identical electrical and functional behavior but reflects updated Freescale packaging and traceability coding. Versus MPC852T, it trades raw speed for deterministic SCC-based serial protocol handling and integrated DRAM control - critical for cost-sensitive, low-power bridge applications.

Availability

KMC68EN302AG25BT is available at Aetrix Electronics and suitable for low-end network bridges, ISDN-to-Ethernet routers, and industrial communication controllers requiring stable component supply across extended product lifecycles.

Supply support for KMC68EN302AG25BT includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Freescale Semiconductor was a U.S.-based semiconductor company specializing in embedded processors, analog, and connectivity solutions before its acquisition by NXP in 2015.

The MC68EN302 product line extends the MC68302 IMP family with integrated Ethernet and DRAM controllers - designed specifically for cost-sensitive, single-chip networking edge devices operating at ≤25 MHz.

FAQ

What is the maximum operating frequency supported by the KMC68EN302AG25BT?

The KMC68EN302AG25BT is rated for 25 MHz operation with 5 V ±5% supply. It supports zero-wait-state access to 80 ns DRAM at this frequency, and its CLKO output delivers a clean, buffered 25 MHz clock signal for system synchronization. The device's timing specifications - including setup/hold times for address/data and strobes - are validated exclusively at this speed grade; operation above 25 MHz is not guaranteed or characterized.

Does the KMC68EN302AG25BT include an integrated Ethernet PHY?

No, the KMC68EN302AG25BT integrates only the Ethernet MAC layer and controller logic - not the physical layer transceiver. It requires an external PHY such as the MC68160 EEST (Twisted Pair/AUI) connected via the RX/TX, RENA/TENA, RCLK/TCLK, and CLSN pins. The MAC implements full IEEE 802.3 compliance, including CSMA/CD, CRC generation/check, and back-to-back frame reception, but relies on external analog circuitry for signal encoding and line driving.

How does the DRAM controller in the KMC68EN302AG25BT manage refresh cycles?

The KMC68EN302AG25BT DRAM controller performs hidden refresh using CAS-before-RAS (CBR) methodology, with programmable refresh period and precharge timing. Refresh is automatically triggered during idle bus cycles and remains transparent to CPU and DMA operations. Two independent RAS lines (RAS0/RAS1) allow interleaved refresh across banks, minimizing impact on active memory access - critical for real-time serial and Ethernet packet processing in the KMC68EN302AG25BT.

Can the KMC68EN302AG25BT operate without external DRAM?

Yes - the KMC68EN302AG25BT contains 1152 bytes of on-chip dual-port RAM usable for code, descriptors, or packet buffers. While external DRAM is required for full Ethernet and SCC buffer depth in production systems, the KMC68EN302AG25BT can execute boot code and handle minimal frame exchange using only internal RAM. This capability enables basic bring-up, JTAG debugging, and firmware validation prior to DRAM initialization.

What serial protocols are supported by the three SCCs in the KMC68EN302AG25BT?

The KMC68EN302AG25BT retains full backward compatibility with the MC68302's three Serial Communications Controllers (SCCs), supporting HDLC, SDLC, Bisync, Async, X.25, and transparent modes. Each SCC features independent baud rate generators, 8-bit or 16-bit timers, and full-duplex operation. Their register-mapped interface follows the standard 68302 programming model - allowing reuse of existing driver stacks for ISDN, Modbus, or proprietary serial protocols in KMC68EN302AG25BT-based designs.