81C55 View Datasheet(PDF) - Oki Electric Industry

Part Name

Description

Manufacturer

81C55

2048-Bit CMOS STATIC RAM WITH I/O PORTS AND TIMER

Oki Electric Industry 

¡ Semiconductor

MSM81C55-5RS/GS/JS

OPERATION

Description

The MSM81C55-5 has three functions as described below.

• 2K-bit static RAM (256 words ¥ 8 bits)

• Two 8-bit I/O ports (PA and PB) and a 6-bit I/O port (PC)

• 14-bit timer counter

The internal register is shown in the figure below, and the I/O addresses are described in the

table below.

8 Bit Internal Data Bus

Command

Status

PC

PB

PA

Timer Timer

MSB LSB

Timer Mode

6 Bit

8 Bit

8 Bit

I/O Address

A7 A6 A5 A4 A3 A2 A1 A0

¥¥¥¥¥000

¥¥¥¥¥001

¥¥¥¥¥010

¥¥¥¥¥011

¥¥¥¥¥100

¥¥¥¥¥101

¥: Don't care.

Selecting Register

Internal command/status register

Universal I/O port A (PA)

Universal I/O port B (PB)

I/O port C (PC)

Timer count lower position 8 bits (LSB)

Timer count upper position 6 bits and timer mode

2 bits (MSB)

10/19

Share Link: