Measurement Computing PCI-DIO96 - Manual (Page 15)

PCI-DIO96 User's Guide Functional Details
15
Signal level control
All the digital inputs on the PCI-DIO96 are 8255 CMOS TTL. The PCI-DIO96 output signals are 8255 CMOS.
Note
The 82C55 digital I/O chip initializes all ports as inputs on power- up and reset. A TTL input is a high
impedance input. If you connect another TTL input device to the 82C55 it could be turned ON or OFF every
time the 82C55 is reset. Remember, the 82C55 is reset to the INPUT mode.
On power up and reset, all I/O bits are set to input mode. If you are using the board to control items that must
be OFF on reset, install pull-down resistors. The PCI-DIO96 has open locations where you can install Single
Inline Packages (SIP) resistor networks in either pull-up or pull-down configurations (refer to Figure 4).
Figure 4. Open locations for SIP packs
You can install pull-up and pull-down resistor SIP packs at PORT #A, PORT #B, and PORT #C. These ports
are adjacent to the I/O connector. When installed, the SIP establishes either a high or low logic level at each of
the eight I/O lines on the port.