National Instruments NI PCIe-8255R User Manual

Also see for NI PCIe-8255R: Quick start guide Getting started Quick start guide

National Instruments NI PCIe-8255R User Manual Manual pdf 28 page image

Transmission Line EffectsTransmission line effects can degrade the signals on the I/O cables andcause instability. To minimize transmission line effects, use twisted pairwires with a characteristic impedance of 118 Ω to connect external signalsto the 44-pin I/O D-SUB connector.Figure 2-8 shows connections to the 44-pin D-SUB connector thatminimize transmission line effects.Figure 2-8. Connections to the 44-pin D-SUB connector that minimizetransmission line effectsWhen connecting to TTL inputs on the NI 8255R, match the outputimpedance of the transmitting device to the characteristic impedance of thecable. For example, if the cable characteristic impedance is 118 Ω, makeR s equal to 118 Ω, as shown in the Figure 2-8.TTL OUT(0) ReceivingEquipmentTTL IN(0)118 Ω44-PinDSUB3211762 kΩTransmittingEquipmentR S+5 VNI 8255R