National Instruments 653 Series User Manual

Also see for 653 Series: User guide

Contents

National Instruments 653 Series User Manual Manual pdf 23 page image

Chapter 2 Using Your NI 653X© National Instruments Corporation 2-3 NI 653X User ManualUsing the open-collector driver has the following advantages:• It connects two or more open-collector outputs together withoutdamaging the drivers.• It connects open collector outputs to open-collector drivers, to GNDsignals, or to switches connecting to GND signals, without damagingthe drivers.• It uses open collector outputs bidirectionally; if you connectopen-collector outputs together, you can read back the value of a pin todetermine if any connected outputs are logic low.Using Control Lines as Extra Unstrobed Data LinesThe NI 653X has two timing controllers (Group 1 and Group 2) forhigh-speed data transfer. Each group contains four control lines which cantime the input/output of data with hardware precision. You can use Groups1 and 2 to perform the following actions:• Generate or receive digital patterns and waveforms at regular intervalsor timed by an external TTL signal• Transfer data between two devices using one of six configurablehandshaking protocols• Acquire digital data every time the state of a data line changesNote If you configure either group to perform handshaking I/O or pattern I/O, theassociated timing control lines for that group are not available for unstrobed I/O.If you are not using Group 1 and/or Group 2 as timing controllers toperform pattern I/O or handshaking I/O, you can use their control lines asextra data lines. These lines constitute Port 4. The direction and outputdriver type of these lines are not configurable—four lines are used as inputonly and four are used as standard output only. Even though there are eightactual lines, the port width for Port 4 is 4 bits. In software, these lines arecollectively referred to as Port 4. When writing to Port 4, the output linesare affected; and when reading from Port 4, the input lines are read.Table 2-1 displays how Port 4 lines are organized.