NXP Semiconductors SC28L194A1A,518

Overview

SC28L194A1A,518 from NXP Semiconductors (formerly Philips) is a quad-channel CMOS UART IC supporting simultaneous 3.3 V and 5 V operation, featuring four independent full-duplex asynchronous serial channels, 16-byte transmit/receive FIFOs per channel, programmable baud rates up to 500 kbaud, and hardware/software flow control (RTS/CTS + XON/XOFF). It serves as a high-density serial interface controller in industrial terminal servers and data concentrators.

For engineers reviewing the SC28L194A1A,518 datasheet, SC28L194A1A,518 pinout, SC28L194A1A,518 application, or SC28L194A1A,518 equivalent, this device delivers deterministic interrupt arbitration, multi-drop address recognition, and synchronous host bus timing - critical for legacy RS-232/422 systems requiring reliable multi-channel serial expansion with minimal CPU overhead.

Technical Context

The SC28L194A1A,518 integrates four independent UART channel blocks sharing a common timing subsystem comprising a 2–8 MHz crystal oscillator, fixed-rate baud rate generator (22 standard rates), and two 16-bit programmable counters for non-standard baud generation. Each channel supports fully configurable data formats (5–8 data bits, 1/1.5/2 stop bits, odd/even/no parity) and includes dedicated change-of-state detectors on all I/O pins.

Its synchronous host interface operates at up to 33 MHz SCLK with 4-cycle bus cycles and supports both asynchronous (CEN-gated) and burst-mode synchronous access. Interrupt arbitration resolves up to 64 sources across channels using FIFO fill/empty levels, error conditions, and character recognition events - reporting context via a Current Interrupt Register (CIR) that drives vectored interrupt vectors.

Key Specifications

Pinout & Package

SC28L194A1A,518 is housed in a 68-pin Plastic Leaded Chip Carrier (PLCC, SOT188-2) with 4 V_{SS_IC}, 4 V_{CC_I}, 4 V_{SS_O}, 2 V_{CC_O}, and 2 V_{CC_C} power pins for noise isolation between input-sensitive, output-driver, and core logic domains.

Key Features

Applications

Equivalent & Alternatives

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

Compared with EXAR XR16L788IQ-F and Maxim MAX3107ETJ+, the SC28L194A1A,518 uniquely balances 4-channel density, 68-pin PLCC compatibility, and synchronous parallel bus timing - making it irreplaceable in legacy industrial backplanes where board real estate and interface continuity constrain upgrade paths.

Availability

SC28L194A1A,518 is available at Aetrix Electronics and suitable for industrial terminal servers, data concentrators, and ISDN front ends requiring stable component supply across extended product lifecycles.

Supply support for SC28L194A1A,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 acquired Philips Semiconductors in 2006 and continues its legacy of high-reliability interface ICs for industrial and communications infrastructure.

The SC28L194A1A,518 belongs to NXP's legacy UART family designed specifically for robust multi-channel serial expansion in mission-critical industrial control, telecommunications, and instrumentation systems.

FAQ

What is the maximum baud rate supported by the SC28L194A1A,518?

The SC28L194A1A,518 supports up to 500 kbaud using its programmable BRG timers. Standard fixed rates reach 460.8 kbaud (e.g., with 7.3728 MHz crystal), and non-standard rates up to 500 kbaud are achievable via timer reload values. The SC28L194A1A,518 achieves this by generating 16× oversampled clocks internally - critical for accurate bit sampling at high speeds.

Does the SC28L194A1A,518 support both 3.3 V and 5 V operation simultaneously?

Yes - the SC28L194A1A,518 uses segregated power domains: V_{CC_I}/V_{SS_IC} for input-sensitive logic, V_{CC_O}/V_{SS_O} for high-current drivers, and V_{CC_C} for core logic. This allows safe coexistence of 3.3 V and 5 V signaling on the same device without level shifters. The SC28L194A1A,518 datasheet specifies operation at either 3.3 V ±10% or 5.0 V ±10%, but not mixed rail voltages on the same supply pin group.

How does interrupt arbitration work in the SC28L194A1A,518?

The SC28L194A1A,518 uses a priority-encoded bidding system across 64 interrupt sources (e.g., RX FIFO fill level, TX FIFO empty, error flags). Each source generates a 4-bit "bid" based on FIFO status; the highest bid exceeding a user-defined threshold triggers IRQN. On IACKN, the Current Interrupt Register (CIR) captures channel, source type, and fill level - enabling direct vectoring to handler code. This eliminates polling and ensures deterministic latency for the SC28L194A1A,518.

Can the SC28L194A1A,518 operate without an external crystal?

Yes - the SC28L194A1A,518 accepts an external clock (100 kHz–10 MHz) on X1/CCLK with X2 left unconnected. The internal oscillator is optional; the baud rate generator and timers derive timing from X1 regardless of source. However, crystal operation (2–8 MHz) is recommended for stability in temperature-varying environments. The SC28L194A1A,518 maintains full functionality with either clock source.

What is the purpose of the "Change of State Detectors" on I/O pins?

Each of the 16 I/O pins (I/O0–3 per channel) includes a hardware change-of-state detector that flags transitions (0→1 or 1→0) after 25–50 µs debounce. These generate interrupts independently of UART activity - useful for monitoring modem control lines (DCD, DSR) or external event inputs. The SC28L194A1A,518 reports these via dedicated status bits, enabling responsive host reaction without continuous polling.