NXP Semiconductors SCC2691AC1A28,602

Overview

SCC2691AC1A28 from NXP Semiconductors (formerly Philips Semiconductors) is a CMOS-LSI universal asynchronous receiver/transmitter (UART) providing full-duplex serial communication with quadruple-buffered receiver, independent receiver/transmitter baud rate selection, and 16-bit programmable counter/timer. It operates from a single +5 V supply, supports 5–8 data bits with parity, and targets industrial terminal systems requiring dual-speed channel operation.

For engineers reviewing the SCC2691AC1A28 datasheet, SCC2691AC1A28 pinout, SCC2691AC1A28 application, or SCC2691AC1A28 equivalent, key selection criteria include its 28-pin PLCC package, TTL-compatible I/O, 18 fixed baud rates up to 115.2 kbaud, power-down mode reducing current to 500 µA, and support for automatic RTS flow control via MPI/MPO handshaking.

Technical Context

The SCC2691AC1A28 implements a fully integrated UART with independent clock selectors for receiver and transmitter, enabling simultaneous operation at different baud rates-critical for clustered terminal or multi-processor address-frame wake-up applications. Its 16-bit counter/timer serves both as baud rate source and general-purpose timing resource, configurable via auxiliary control register (ACR) bits [6:4] and output-selectable on MPO.

Receiver architecture includes a 3-deep FIFO with status-strobed parity/framing/overrun detection per character, false start bit rejection, and line break generation/detection. Transmitter supports automatic break insertion, local/remote loopback modes, and TxRDY signaling-all accessible via eight memory-mapped registers selected by A0–A2 under CEN/WRN/RDN control.

Key Specifications

Pinout & Package

SCC2691AC1A28 is housed in a 28-pin Plastic Leaded Chip Carrier (PLCC) package with J-lead configuration, compatible with standard PLCC sockets and reflow soldering profiles for industrial PCB assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SCC2691AC1A28, SCC2692AC1A28 delivers dual-channel capability at the expense of increased software complexity, while SCN2681C1A28 offers lower cost and footprint compatibility but sacrifices baud rate flexibility and advanced handshaking-making SCC2691AC1A28 optimal for new industrial designs demanding configurability and power efficiency.

Availability

SCC2691AC1A28 is available at Aetrix Electronics and suitable for industrial terminal systems, multi-drop serial networks, legacy equipment retrofit, and embedded diagnostic interfaces requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SCC2691AC1A28 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 leader focused on secure connectivity solutions for automotive, industrial, and IoT applications, with roots in Philips' pioneering analog and mixed-signal design heritage.

The SCC2691AC1A28 belongs to NXP's legacy communications IC portfolio, engineered specifically for robust, low-power asynchronous serial interfacing in harsh industrial environments where reliability, long-term availability, and TTL compatibility are critical.

FAQ

What is the maximum baud rate supported by the SCC2691AC1A28?

The SCC2691AC1A28 supports a maximum baud rate of 115.2 kbaud using either its internal 18-rate table or non-standard rates derived from the 16-bit counter/timer. External 1X or 16X clock inputs allow operation beyond this limit, constrained only by AC timing specifications such as tRXS (100 ns setup) and fRX (≤3.6864 MHz for 16X mode). The SCC2691AC1A28 achieves this while maintaining full framing integrity for 5–8 data bits, parity, and 1/1.5/2 stop bits.

Does the SCC2691AC1A28 support hardware flow control?

Yes, the SCC2691AC1A28 supports hardware flow control through its multi-purpose I/O pins. When configured via the auxiliary control register, the MPO pin outputs RTSN (Request to Send), which automatically deasserts when the 3-character receiver FIFO is full and reasserts upon space availability. The MPI pin accepts CTSN (Clear to Send) input, enabling end-to-end handshake coordination without CPU intervention-ensuring zero-character loss in high-throughput serial links.

Can the SCC2691AC1A28 operate with an external clock instead of a crystal?

Yes, the SCC2691AC1A28 can operate with an external clock applied to the X1/CLK pin, eliminating the need for a crystal and associated load capacitors. The device accepts frequencies up to 4.0 MHz (per AC specs), and the X2 pin may be left unconnected or grounded. When using external clocking, the SCC2691AC1A28 maintains full functionality-including baud rate generation, counter/timer operation, and interrupt timing-as verified in the clock timing section of the official datasheet.

What is the purpose of the quadruple-buffered receiver in the SCC2691AC1A28?

Quadruple buffering in the SCC2691AC1A28 comprises a 3-character FIFO plus the receive shift register, significantly reducing the risk of receiver overrun during burst data reception and lowering interrupt servicing frequency in CPU-limited systems. This architecture allows the host processor to service incoming characters at relaxed intervals-especially valuable in interrupt-driven embedded applications where latency must be minimized and deterministic response guaranteed for each received byte.

Is the SCC2691AC1A28 compatible with modern 3.3 V microcontrollers?

The SCC2691AC1A28 is a +5 V TTL-compatible device with input thresholds (VIL = 0.8 V, VIH = 2.0 V) and output drive levels (VOH ≥ 2.4 V @ –400 µA) that meet standard TTL specifications. Direct connection to 3.3 V microcontrollers is not recommended without level translation, as its outputs exceed 3.3 V absolute maximum ratings and its inputs require ≥2.0 V for logic high recognition. For mixed-voltage systems, the SCC2691AC1A28 should be paired with bidirectional level shifters or buffer ICs to ensure safe interoperability.