NXP Semiconductors SCC2691AC1D24,518

Overview

SCC2691AC1D24,518 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 SCC2691AC1D24,518 datasheet, SCC2691AC1D24,518 pinout, SCC2691AC1D24,518 application, or SCC2691AC1D24,518 equivalent, key selection criteria include TTL-compatible 24-pin SOIC package, 22 fixed baud rates up to 115.2 kbaud, receiver FIFO overrun prevention via RTS handshaking, and power-down mode reducing current to 500 µA.

Technical Context

The SCC2691AC1D24,518 implements a fully integrated UART with independent clock selectors for receiver and transmitter paths, enabling true dual-speed operation-e.g., 9600 baud receive / 19200 baud transmit in clustered terminal systems. 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.

Baud generation supports crystal (3.6864 MHz), external 1X/16X clocks, or non-standard rates derived from the programmable timer. The receiver uses 16X oversampling with false start bit detection, framing/parity/overrun error capture, and address-frame recognition mode for multi-processor wake-up-activated by MR1[4:3] = '11'.

Key Specifications

Pinout & Package

SCC2691AC1D24,518 is housed in a 24-pin plastic small outline large (SOL) package (SOT137-1), pin-compatible with industry-standard 300-mil DIP footprints but offering surface-mount reliability and thermal performance for industrial PCBs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SCC2691AC1D24,518, SCC2692AC1D24 offers greater buffer depth and speed for modern firmware update protocols, while MAX3100EAP+ trades parallel interface complexity for SPI integration and ESD resilience-making each optimal for distinct architecture trade-offs.

Availability

SCC2691AC1D24,518 is available at Aetrix Electronics and suitable for industrial terminal systems, legacy equipment interface, multi-processor networks, and embedded diagnostic ports requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SCC2691AC1D24,518 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 delivering high-performance mixed-signal solutions for automotive, industrial, and IoT applications, with roots in Philips Semiconductors' pioneering communications IC portfolio.

The SCC2691AC1D24,518 belongs to NXP's legacy UART product line designed specifically for industrial-grade serial communication in harsh environments-emphasizing reliability, wide temperature operation, and backward compatibility with 1980s–1990s embedded systems.

FAQ

What is the maximum baud rate supported by the SCC2691AC1D24,518?

The SCC2691AC1D24,518 supports up to 115.2 kbaud using its internal baud rate generator or external clock inputs. Non-standard rates can be achieved via the 16-bit programmable counter/timer, with timing constraints limiting practical operation to ≤115.2 kbaud under standard 3.6864 MHz crystal drive. The device does not support rates beyond this limit in production-tested configurations.

Does the SCC2691AC1D24,518 support automatic hardware flow control?

Yes, the SCC2691AC1D24,518 supports automatic RTS/CTS flow control. When configured via the auxiliary control register, the MPO pin functions as RTSN and is automatically negated when the 3-character receiver FIFO becomes full. It reasserts when space becomes available-enabling seamless handshaking with external modems or transceivers without CPU intervention.

Can the SCC2691AC1D24,518 operate with an external clock instead of a crystal?

Yes, the SCC2691AC1D24,518 accepts an external clock signal on the X1/CLK pin, ranging from 0 to 4.0 MHz. When using external clocking, X2 may be left unconnected or grounded. The device's timing circuits-including baud generation, counter/timer, and internal logic-derive all timing references directly from this input, eliminating crystal load capacitance requirements.

What is the function of the MPI pin on the SCC2691AC1D24,518?

The MPI pin on the SCC2691AC1D24,518 is a multi-purpose input configurable as Clear-to-Send (CTSN), counter/timer external clock (CTCLK), or receiver/transmitter external clock (RTCLK). It features an internal VCC pull-up (1–4 µA) and is sampled synchronously to support precise timing-critical functions like external baud synchronization or event-triggered counter starts.

How does the power-down mode affect register retention in the SCC2691AC1D24,518?

In power-down mode, the SCC2691AC1D24,518 freezes the internal crystal oscillator while preserving all register contents-including mode, control, status, and counter/timer values. This allows immediate resumption of UART operation upon exit, with no reinitialization required. Current drops to ≤500 µA, making it suitable for battery-backed diagnostic or watchdog applications.