W78E51B 8-BIT MTP MICROCONTROLLER is an introduction document of W78E51B chip, which is an 8-bit microcontroller with low power consumption and wide frequency range.
The W78E51B is an 8‑bit CMOS microcontroller compatible with the standard 8051 instruction set. It features a 4 KB multiple‑time‑programmable ROM, 128 bytes of on‑chip RAM, four 8‑bit bi‑directional I/O ports, an additional 4‑bit port, two 16‑bit timer/counters, a full‑duplex UART, and a watchdog timer. The device operates from a 4.5 V to 5.5 V supply and offers idle and power‑down power‑reduction modes.
The manual details pin assignments, register maps, interrupt sources, power‑management registers, and programming procedures for the MTP‑ROM. It also includes package dimensions for DIP‑40, PLCC‑44, and PQFP‑44 variants, as well as typical application circuits and EMI‑reduction techniques.
| Supply voltage | 4.5 V to 5.5 V |
|---|---|
| MTP ROM size | 4 KB |
| RAM size | 128 bytes |
| 8‑bit I/O ports | Four ports |
| Extra 4‑bit I/O port | P4.0‑P4.3 |
| Timers | Two 16‑bit timer/counters |
| Serial port (UART) | Full‑duplex UART |
| Watchdog timer | Enabled, with prescaler |
| Package types | DIP‑40, PLCC‑44, PQFP‑44 |
The microcontroller provides two power‑reduction modes: idle mode and power‑down mode, both selectable by software.
Set bit 0 (AO) of the AUXR register at address 08Eh to disable the ALE output.