The Measurement Computing CIO-DIO24 is a digital input/output board for ISA-based PC systems delivering 24 individually programmable I/O lines. Built around the Intel 82C55 Programmable Peripheral Interface chip, it provides flexible I/O configuration—two 8-bit ports plus one 8-bit port (divisible into two 4-bit ports)—each software-selectable for input or output operation. All signals connect via a single 37-pin D-type connector. The board occupies one half-size ISA slot and operates at CMOS/TTL logic levels, with all I/O bits defaulting to input mode (high impedance) on power-up.
Technical Specifications
• Digital I/O Lines: 24 total
• Interface Chip: Intel 82C55 Programmable Peripheral Interface (PPI)
• I/O Configuration: Two 8-bit ports (A, B) and one 8-bit port (C); Port C subdivides into 4-bit segments (C-HI, C-LO); each port individually programmable for input or output
• Logic Levels: CMOS/TTL compatible
– Input High: 2.0 V minimum, 7.0 V maximum
– Input Low: -0.5 V minimum, 0.8 V maximum
– Input Impedance: High impedance (74LS characteristic)
• Output Drive (CIO-DIO24): 1.7 mA sink @ 0.45 V; 200 µA source @ 2.4 V
• Output Drive (CIO-DIO24H): 64 mA sink; 15 mA source
• Power Consumption at +5V:
– CIO-DIO24: 170 mA typical / 270 mA maximum
– CIO-DIO24H: 400 mA typical / 625 mA maximum
– Key Features
• Individual software control of all 24 I/O lines
• Mode 0 (82C55) operation for straightforward digital switching
• Optional pull-up or pull-down resistor installation for custom reset behavior
• Compact half-size board footprint for space-constrained systems
– Typical Applications
• Industrial process control and machine interfacing
• Data acquisition with digital switching logic
• Relay and solenoid activation circuits
• Real-time digital signal monitoring and response
– Compatibility & Integration
• ISA bus interface for IBM PC/XT/AT compatible systems
• 37-pin connector for external signal access
• Standard PC power supply (+5 V) with provision for external load power on connector pins
