NXP Semiconductors SCC2691AC1A28,623

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 TTL-compatible 28-pin PLCC packaging, 22 fixed baud rates up to 115.2 kbaud, receiver FIFO overrun prevention via RTS handshake, power-down mode with register retention, and support for crystal or external clock inputs at X1/CLK and X2.

Technical Context

The SCC2691AC1A28 implements a fully independent dual-clock architecture: the receiver and transmitter each select timing sources from the on-chip baud rate generator (18 fixed rates), 16-bit counter/timer, or external 1X/16X clocks - enabling true dual-speed operation in clustered terminal systems. Its quadruple-buffered receiver FIFO reduces interrupt overhead and prevents overrun by asserting RxRDY/FFULL and controlling remote transmitter via MPO-configured RTSN.

Timing control is centralized around a crystal oscillator (3.6864 MHz nominal) or external clock input at X1/CLK, feeding both the baud rate generator and the multi-function 16-bit counter/timer. The counter/timer supports timer mode (square-wave output) and counter mode (terminal-count interrupt), with output selectable on MPO via ACR[2:0], while MPI provides configurable inputs including CTSN, CTCLK, and RTCLK.

Key Specifications

Pinout & Package

SCC2691AC1A28 uses a 28-pin PLCC (SOT261-2) package with gull-wing leads, 1.27 mm pitch, and body size 11.5 × 11.5 mm. Pin 1 is located at the index corner adjacent to the notch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SCC2691AC1A28, SCC2692AC1A28 delivers higher FIFO depth and extended speed but requires firmware adaptation, while ST16C2550CJ44 offers voltage flexibility and integrated flow control at the cost of package size and pin count - making SCC2691AC1A28 optimal for cost-sensitive, space-constrained industrial retrofits.

Availability

SCC2691AC1A28 is available at Aetrix Electronics and suitable for industrial terminal systems, legacy equipment interface, multi-processor wake-up networks, and embedded diagnostic subsystems 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 IC development.

The SCC2691AC1A28 belongs to NXP's legacy communications interface product line, designed specifically for robust, low-power asynchronous serial communication in industrial control, point-of-sale, and terminal equipment where reliability and long-term availability are critical.

FAQ

What is the maximum baud rate supported by the SCC2691AC1A28?

The SCC2691AC1A28 supports up to 115.2 kbaud using its internal baud rate generator or external clock inputs. While the datasheet lists 22 fixed rates up to that value, non-standard rates - including those exceeding 115.2 kbaud - are achievable via the programmable 16-bit counter/timer or direct external 1X/16X clock injection at the X1/CLK pin, subject to timing constraints in the AC Electrical Characteristics table.

Does the SCC2691AC1A28 support automatic hardware flow control?

The SCC2691AC1A28 does not implement autonomous RTS/CTS handshaking in hardware. However, it provides the necessary signals - RxRDY/FFULL status on MPO and CTSN input on MPI - enabling firmware-driven flow control. When configured, the UART asserts RxRDY/FFULL upon FIFO fill, allowing the host CPU to drive RTSN low via MPO to disable the remote transmitter and prevent overrun.

Can the SCC2691AC1A28 operate with a 3.3 V supply?

No. The SCC2691AC1A28 is specified exclusively for +5 V ±10% operation, with absolute maximum ratings and DC electrical characteristics defined only for that voltage range. Its I/O structure, internal logic thresholds, and power-down behavior are optimized for 5 V TTL compatibility; operation at 3.3 V is not guaranteed and may result in functional failure or parametric violation.

How does the receiver FIFO in the SCC2691AC1A28 prevent data loss?

The SCC2691AC1A28 implements a three-character deep FIFO with dedicated FFULL status flag and RxRDY interrupt. When the FIFO fills, the device can assert RxRDY/FFULL on MPO (configured as open-drain output) to signal the remote transmitter to halt via RTS/CTS handshake. This hardware-assisted flow control, combined with quadruple buffering, minimizes the risk of overrun during high-speed reception or delayed CPU servicing.

Is the SCC2691AC1A28 pin-compatible with other UARTs in the SCC26xx family?

Yes - the SCC2691AC1A28 shares identical 28-pin PLCC pinout and register mapping with SCC2692AC1A28 and SCC2698BAC1A28. However, functional differences exist: SCC2692 adds 16-byte FIFO and extended interrupts, while SCC2698B integrates dual-channel operation. Direct substitution is electrically safe but requires firmware verification for feature-specific register usage and interrupt handling.