NXP Semiconductors MC68EN302AG25BT

Overview

MC68EN302AG25BT from Freescale is an integrated multiprotocol processor combining a 68000-compatible CPU core, three serial communication controllers (SCCs), a full IEEE 802.3-compliant Ethernet controller, DRAM controller, and JTAG debug interface - all in a single 144-pin TQFP package operating at 25 MHz with 5 V supply. It targets embedded networking bridges and ISDN-to-Ethernet routers requiring deterministic real-time protocol handling and glueless DRAM interfacing.

For engineers reviewing the MC68EN302AG25BT datasheet, MC68EN302AG25BT pinout, MC68EN302AG25BT application, or MC68EN302AG25BT equivalent, key selection considerations include its 16-bit Ethernet bus interface, dual 128-byte Tx/Rx FIFOs, 128 on-chip buffer descriptors, IEEE 1149.1 JTAG compliance, and support for up to 8 MB per DRAM bank with programmable refresh timing.

Technical Context

The MC68EN302AG25BT extends the MC68302 architecture with a dedicated Ethernet controller that operates independently of the three legacy SCCs, using two dedicated DMA channels and a dual-port RAM for descriptor management. Its Ethernet protocol core handles full-duplex 10 Mbps operation (20 Mbps in switched mode), automatic collision retransmission, and frame flushing without CPU intervention.

The DRAM controller supports two independent banks with separate RAS/CAS lines, address multiplexing, programmable wait states (zero-wait at 25 MHz with 80 ns DRAM), and hidden refresh - coordinated via the module bus controller, which also manages interrupt routing for Ethernet and DRAM blocks and external bus master arbitration.

Key Specifications

Pinout & Package

MC68EN302AG25BT is housed in a 144-lead thin quad flat pack (TQFP) with 0.5 mm lead pitch and exposed thermal pad. Pin functions are defined across multiple I/O groups including parallel address/data buses (A23–A1, D15–D0), peripheral control signals (RX/TX/RENA/CLSN/TENA/TCLK), DRAM interface (RAS0/RAS1/CAS0/CAS1/DRAMRW), and JTAG test access (TMS/TCK/TDO/TDI/TRST).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MC68302AC25B, the MC68EN302AG25BT integrates Ethernet and DRAM control to reduce component count and board space, while MC68EN360CZP25 offers architectural advancement at the cost of compatibility - making MC68EN302AG25BT optimal for cost-constrained, fixed-function embedded bridges where legacy 68k toolchains and deterministic SCC timing remain critical.

Availability

MC68EN302AG25BT is available at Aetrix Electronics and suitable for low-end network bridges, ISDN-to-Ethernet routers, and industrial communication controllers requiring stable component supply and long-term obsolescence management.

Supply support for MC68EN302AG25BT 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 (now part of NXP Semiconductors) was a leading designer of embedded processors and analog/mixed-signal ICs for automotive, industrial, and networking applications.

The MC68EN302AG25BT belongs to Freescale's 68k-based Integrated Multiprotocol Processor family, engineered specifically for cost-sensitive, real-time embedded networking systems requiring protocol flexibility without external glue logic.

FAQ

What is the maximum Ethernet data rate supported by the MC68EN302AG25BT?

The MC68EN302AG25BT supports IEEE 802.3-compliant 10 Mbps baseband Ethernet operation. In full-duplex (switched) mode, it achieves 20 Mbps aggregate throughput - 10 Mbps transmit and 10 Mbps receive simultaneously - with no CPU overhead due to autonomous collision handling and dual 128-byte FIFOs. This is confirmed in the Ethernet Features section of the official product brief.

Does the MC68EN302AG25BT include an on-chip DRAM controller, and what are its key capabilities?

Yes, the MC68EN302AG25BT integrates a DRAM controller derived from the MC68306, supporting two independent banks with separate RAS/CAS lines, address multiplexing, programmable wait states (zero-wait achievable with 80 ns DRAM at 25 MHz), and hidden refresh cycles. Each bank is configurable from 128 KB to 8 MB, and write protection is programmable - eliminating need for external DRAM interface logic.

How many serial communication channels does the MC68EN302AG25BT provide, and what types are they?

The MC68EN302AG25BT provides four serial communication channels: three fully compatible Serial Communication Controllers (SCCs) inherited from the MC68302, plus one dedicated Ethernet channel. The SCCs support protocols including HDLC, SDLC, UART, and bisync, while the Ethernet channel implements full IEEE 802.3 MAC-layer functionality - enabling simultaneous ISDN, modem, and LAN connectivity in a single chip.

Is the MC68EN302AG25BT pin-compatible with the standard MC68302 series?

No, the MC68EN302AG25BT is not pin-compatible with the MC68302. It uses a 144-pin TQFP package versus the MC68302's 132-pin PQFP, and introduces new pins for Ethernet (RX/TX/RENA/CLSN/TENA/TCLK), DRAM control (RAS0/RAS1/CAS0/CAS1/DRAMRW), and JTAG (TMS/TCK/TDO/TDI/TRST). Layout redesign is required when upgrading from MC68302 to MC68EN302AG25BT.

What debug and test capabilities does the MC68EN302AG25BT offer?

The MC68EN302AG25BT includes full IEEE 1149.1 JTAG boundary-scan support via dedicated TMS, TCK, TDO, TDI, and TRST pins. This enables production-level structural testing, in-circuit debugging, and emulation without requiring additional probe points. The JTAG module is functionally identical to that in the MC68302 but extended to cover newly added Ethernet and DRAM logic blocks - verified in the Module Bus Controller and Testing sections of the product brief.