GPIO-104

The GPIO-104 is an 8-bit analog and digital input/output module designed to satisfy a broad range of applications. Its generous assortment of functions and capabilities will, in many instances, make the GPIO-104 the only peripheral module required. It conforms to the PC/104 standard, operates on just +5V power, and uses a single 50-Position IDC header for all off-board I/O signal connections.

Analog Inputs

Eight 12-bit single-ended analog inputs are provided, each with software programmable input ranges of ±10V, ±5V, +5V, +10V. This capability effectively increases the dynamic range to 14-bits when employing software range-switching techniques. Input protection handles applied voltages up to ±16.5V and continues to function even when power is off. In addition, a fault condition on any input channel will not affect the operation of the remaining channels.

A special feature of the Analog-to-Digital Converter is its ability to allow the separate acquisition and conversion times be individually controlled by the user's software or automatically sequenced by the GPIO-104 hardware. Overall timing is precisely maintained by a crystal oscillator.

Analog-To-Digital conversions are initiated by writing a control byte which selects the input channel and sets its range along with other parameters. The host can determine when the conversion is complete using one of three methods: by simply waiting longer than the conversion time, by polling a status flag or by having the status flag interrupt the host when it becomes set. The resulting 12-bit value is read as two bytes in an 8+4 format.

Analog Outputs

The four 12-bit analog outputs are individually hardware programmable to provide one of three popular output ranges: ±5V, +5V, +10V. An on-board DC/DC converter enables the bipolar and +10V ranges to be achieved even though the GPIO-104 operates using only the PC/104 Bus +5V power supply.

The GPIO-104 includes the capability of having all the outputs update simultaneously by means of a single software write command. Those channels pre-loaded with new data will change, while the remaining channels maintain their previous output voltages glitch-free. This feature is particularly useful in applications which can not tolerate phasing errors between the outputs. The 12-bit data is loaded into the DACs using an 8+4 bit format.

Digital I/O

An industry standard 82C55 Programmable Peripheral Interface chip provides 24 digital channels across three 8-bit ports. This device offers very flexible configuration, including software programmable port directions and strobed handshaking. Each channel has a 10k pull-up resistor and defaults to logic "1" and input mode during system reset.