• Compatible With: Intel 8155 / 81C55
• Device Type: CMOS RAM, I/O Port, and Timer Combination IC
• Package Type: 40-Pin DIP

General Features

• Combines three functions in one IC:
  • 256 × 8 Static RAM
  • 22 Programmable I/O Lines
  • 14-Bit Programmable Timer
• CMOS low-power design
• Direct interface to 8085, 8086, Z80, and similar microprocessors
• Software programmable operation

Memory Section

• RAM Capacity: 256 Bytes
• Organization: 256 × 8 bits
• Static memory (no refresh required)
• Read/write memory

I/O Ports

• Total I/O Lines: 22

Port configuration:

• Port A: 8 bits
• Port B: 8 bits
• Port C: 6 bits

Features:

• Programmable input/output
• TTL-compatible signals
• Bit-programmable operation

Timer Section

• Timer Width: 14 bits
• Programmable interval timer
• One-shot and periodic timing applications
• Interrupt generation capability

Electrical Characteristics

• Supply Voltage:
  • 4.5 V to 5.5 V
  • Nominal: 5 V
• CMOS low-power operation
• TTL-compatible inputs and outputs

CPU Interface

• 8-bit data bus
• Address bus interface
• Read/Write control signals
• Chip Select input

Compatible with:

• Intel 8085
• Intel 8086
• Zilog Z80

Package

• Package Type: PDIP
• Pin Count: 40 Pins
• Mounting Style: Through-Hole

Operating Temperature

• Commercial versions:
  • 0°C to +70°C

Key Features

• 256-byte SRAM
• 22 programmable I/O lines
• 14-bit timer
• Single-chip peripheral solution
• Low power CMOS technology
• Microprocessor compatible
• Reduces system component count

Typical Applications

• Industrial controllers
• Embedded systems
• Data acquisition equipment
• Telecommunications systems
• Test instruments
• Single-board computers
• Microprocessor training systems
• Process control equipment

Functional Blocks

• Static RAM
• I/O Port A (8-bit)
• I/O Port B (8-bit)
• I/O Port C (6-bit)
• 14-bit Timer
• Bus Interface Logic
• Control Registers