NXP Semiconductors SCC68681E1A44,529

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 control backplanes and legacy embedded systems requiring robust RS-232/RS-422 interface management.

For engineers reviewing the SCC68681E1A44 datasheet, SCC68681E1A44 pinout, SCC68681E1A44 application, or SCC68681E1A44 equivalent, key selection criteria include independent baud rate programming per channel, hardware flow control via RTS/CTS, crystal oscillator integration (X1/X2), 44-pin PLCC mechanical compatibility, and interrupt vectoring support for S68000-family microprocessors.

Technical Context

The SCC68681E1A44 implements two fully 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 includes an on-chip crystal oscillator (X1/CLK, X2), a baud rate generator producing 22 fixed rates (50–115.2 kbaud), and a 16-bit counter/timer usable as timer, counter, or timeout monitor. Clock selection logic allows each receiver and transmitter to source timing independently from BRG, counter/timer, or external 1×/16× clocks - critical for multidrop wake-up and dual-speed terminal clustering.

Key Specifications

Pinout & Package

SCC68681E1A44 is housed in a 44-lead PLCC (SOT187-2) package with J-type leads, designed for industrial-grade thermal and mechanical reliability. Pin 44 is VCC (+5 V), Pin 22 is GND, and Pins 32 (X1/CLK) and 33 (X2) support direct crystal connection (e.g., 3.6864 MHz) or external clock input.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SCC68681C1A44, the SCC68681E1A44 provides guaranteed operation across –40 °C to +85 °C and wider supply tolerance, making it essential for ruggedized systems; versus TL16C550CIPN, it delivers true dual-channel independence, integrated counter/timer, and multidrop wake-up - capabilities absent in single-UART alternatives.

Availability

SCC68681E1A44 is available at Aetrix Electronics and suitable for industrial backplane communication, legacy terminal server interface, medical device data logging, and avionics maintenance port applications 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, headquartered in Eindhoven, Netherlands, develops high-performance mixed-signal ICs for automotive, industrial, and communication infrastructure markets, with legacy roots in Philips Semiconductors' MOS-LSI division.

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

FAQ

What is the maximum supported baud rate for 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. The device also permits non-standard rates up to 115.2 kbaud via its 16-bit programmable counter/timer, and achieves 1 MB/sec parallel bus throughput (1× clock mode) or 125 kB/sec (16× clock mode) on the D0–D7 data bus. All timing assumes a nominal 3.6864 MHz crystal on X1/CLK.

Does SCC68681E1A44 include an integrated crystal oscillator?

Yes, the SCC68681E1A44 includes an on-chip crystal oscillator circuit. Pins 32 (X1/CLK) and 33 (X2) are dedicated to connecting a 3.6864 MHz crystal; alternatively, an external clock signal may be applied to X1/CLK while leaving X2 unconnected. The oscillator feeds the baud rate generator, counter/timer, and all internal timing blocks - eliminating the need for external oscillator components in most designs.

How does hardware flow control work on SCC68681E1A44?

Hardware flow control on the SCC68681E1A44 uses OP0/OP1 (RTSAN/RTSBN) and IP0/IP1 (CTSAN/CTSBN). When enabled via mode registers, the DUART automatically asserts RTS upon detecting a valid start bit and deasserts it when the 3-character receiver FIFO reaches capacity. CTS inputs gate transmission: if CTSN goes HIGH mid-transmission, the current character completes but TxDA remains in mark state until CTSN returns LOW. This prevents buffer overrun without CPU intervention.

Can SCC68681E1A44 operate in multidrop networks?

Yes, the SCC68681E1A44 supports multidrop wake-up mode via MR1A[4:3] or MR1B[4:3] = 11. In this mode, the receiver monitors the serial stream continuously - even when disabled - and asserts RxRDY only when an address-tagged character (A/D bit = 1) is received. This allows a master station to broadcast addresses to multiple slaves, waking only the intended target. The A/D bit polarity is programmable per channel via MR1A[2]/MR1B[2].

What package type is used for SCC68681E1A44?

The SCC68681E1A44 uses a 44-lead plastic leaded chip carrier (PLCC) package, designated SOT187-2. It features J-shaped leads for surface-mount assembly and is rated for industrial temperature operation (–40 °C to +85 °C). This package is mechanically and electrically identical to the SCC68681C1A44 variant, differing only in temperature specification and supply voltage tolerance.