NXP Semiconductors SCC68681E1A44,518

Overview

SCC68681E1A44 from NXP Semiconductors (formerly Philips Semiconductors) is a dual-channel CMOS universal asynchronous receiver/transmitter (DUART) in PLCC44 package, supporting independent full-duplex serial communication on Channels A and B with programmable 5–8 data bits, 1/1.5/2 stop bits, odd/even/no parity, and up to 115.2 kbaud. It integrates a 16-bit counter/timer, quadruple-buffered receivers, and multipurpose 6-bit input/8-bit output ports - deployed in industrial terminal systems requiring robust multidrop RS-232/RS-485 interfaces.

For engineers reviewing the SCC68681E1A44 datasheet, SCC68681E1A44 pinout, SCC68681E1A44 application, or SCC68681E1A44 equivalent, key selection considerations include independent baud rate programming per channel, automatic RTS flow control, crystal oscillator integration, 44-pin PLCC mechanical compatibility, and S68000 bus interface support for legacy microprocessor systems.

Technical Context

The SCC68681E1A44 implements two independent UART channels sharing a common 8-bit bidirectional data bus (D0–D7), address decoding (A1–A4), and interrupt architecture. Each channel features separate mode registers (MR1/MR2), status registers (SRA/SRB), and command registers (CRA/CRB), enabling asymmetric configuration - e.g., Channel A at 9600 baud with 8N1 while Channel B runs at 38.4 kbaud with 7E2.

Its timing subsystem combines an on-chip crystal oscillator (X1/CLK, X2), 18 fixed-rate baud generators, and a 16-bit counter/timer that can source 1× or 16× clocks to either receiver or transmitter independently. The receiver FIFO holds three characters with overrun detection, and flow control is implemented via RTS/CTS handshaking using OP0–OP1 (RTSAN/RTSBN) and IP0–IP1 (CTSAN/CTSBN).

Key Specifications

Pinout & Package

SCC68681E1A44 is housed in a 44-lead plastic leaded chip carrier (PLCC44, SOT187-2) with J-lead geometry, designed for surface-mount assembly and socket-compatible insertion. Thermal resistance θ_JA = 50°C/W; moisture sensitivity level (MSL) = 3 per JEDEC J-STD-020.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual UART applications.

Compared with SCC68681C1A44, the SCC68681E1A44 adds industrial temperature range and tighter VCC tolerance (±10%), making it viable for factory-floor deployment; versus TL16C550CIPN, it delivers true dual-channel autonomy, integrated timing resources, and multidrop intelligence - but requires more complex initialization and lacks deep FIFO buffering.

Availability

SCC68681E1A44 is available at Aetrix Electronics and suitable for industrial terminal interfaces, legacy microprocessor communication hubs, RS-485 multidrop network nodes, and automated test equipment serial control requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SCC68681E1A44 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

NXP Semiconductors is a global semiconductor company formed from the spin-off of Philips Semiconductors in 2006, specializing in secure connectivity, automotive, industrial, and IoT solutions with emphasis on long-lifecycle support.

The SCC68681E1A44 belongs to NXP's legacy communications interface product line, originally designed for S68000-family microprocessor systems requiring dual asynchronous serial channels with minimal external components and deterministic interrupt response.

FAQ

What is the maximum baud rate supported by the SCC68681E1A44?

The SCC68681E1A44 supports a maximum data transfer rate of 115.2 kbaud using its internal baud rate generator. This applies to both Channel A and Channel B independently. When operating in 16× clock mode, the maximum serial bit rate remains 115.2 kbaud, with the internal clock running at 1.8432 MHz. External clock inputs may enable non-standard rates up to this limit, but sustained operation beyond 115.2 kbaud is not specified or guaranteed for the SCC68681E1A44.

Does the SCC68681E1A44 include an integrated crystal oscillator?

Yes, the SCC68681E1A44 includes an on-chip crystal oscillator circuit. It requires a 3.6864 MHz crystal connected between pins X1/CLK (32) and X2 (33) to operate. Alternatively, an external 3.6864 MHz clock signal may be applied to X1/CLK while leaving X2 unconnected. The oscillator directly feeds the baud rate generator, counter/timer, and internal logic - eliminating the need for external clock generation circuitry in most designs.

How does hardware flow control work on the SCC68681E1A44?

Hardware flow control on the SCC68681E1A44 uses OP0 (RTSAN) and IP0 (CTSAN) for Channel A, and OP1 (RTSBN) and IP1 (CTSBN) for Channel B. When enabled, the DUART automatically asserts RTS (drives OP0/OP1 LOW) when its receiver FIFO has space, and negates it (drives HIGH) when the FIFO reaches capacity. The remote device monitors CTS (IP0/IP1) to gate transmission. This closed-loop mechanism prevents receiver overrun without CPU intervention - a core feature confirmed in the SCC68681E1A44 datasheet's flow control section.

Can the SCC68681E1A44 operate in multidrop mode, and how is it configured?

Yes, the SCC68681E1A44 supports multidrop mode via its address/data (A/D) bit functionality. It is configured by setting bits MR1A[4:3] or MR1B[4:3] to '11' in the mode register. In this mode, the receiver monitors the serial stream continuously - even when disabled - and asserts RxRDY only upon detecting an A/D bit = 1 (address tag). The CPU then validates the address and enables full reception. This behavior is explicitly documented for the SCC68681E1A44 in the "Multidrop Mode" section of its product data sheet.

What is the purpose of the 6-bit input port and 8-bit output port on the SCC68681E1A44?

These ports provide flexible I/O expansion: the 6-bit input port (IP0–IP5) supports general-purpose reads, change-of-state detection on four pins, and auxiliary functions like external clock inputs (RxCA, TxCB); the 8-bit output port (OP0–OP7) allows individual bit set/reset, status/interrupt signaling (e.g., RxRDYB on OP5), and auto 485 turn-around control (via OP2). Their programmability - detailed in the "Input Port" and "Output Port" sections of the SCC68681E1A44 datasheet - eliminates need for external GPIO expanders in resource-constrained systems.