The AT89S2051/S4051 is a low-voltage, high-performance CMOS 8-bit microcontroller with 2K/4K bytes of In-System Programmable (ISP) Flash program memory. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard MCS-51 instruction set. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89S2051/S4051 is a powerful microcontroller which provides a highly-flexible and cost-effective solution to embedded control applications.
This handbook describes the AT89S2051 and AT89S4051 low‑voltage CMOS 8‑bit microcontrollers, highlighting their 2 KB/4 KB ISP Flash memory, 256 bytes of RAM, 15 programmable I/O lines, two 16‑bit timer/counters, and a full‑duplex enhanced UART. It also covers power‑saving modes, analog comparator, PWM capability, and lock‑bit protection.
The document includes detailed pin‑out diagrams, pin descriptions, reset behavior, clock options (including X2 mode), special function registers, instruction restrictions, and memory lock‑bit settings, providing engineers with the necessary information to integrate and program these devices.
| Flash program memory | 2 KB or 4 KB |
|---|---|
| Internal RAM | 256 bytes (8‑bit) |
| Programmable I/O lines | 15 |
| Timer/Counters | Two 16‑bit |
| Operating voltage range | 2.7 V to 5.5 V |
| Maximum CPU frequency | 24 MHz |
| PWM resolution | 8‑bit |
The devices operate from 2.7 V up to 5.5 V.
Each device provides either 2 KB or 4 KB of ISP Flash program memory.
Both devices have 15 programmable I/O lines.
The microcontrollers contain two 16‑bit timer/counters.