Measurement Computing CIO-DO24DD - Manual (Page 5)

1.0 INTRODUCTION
CIO-DO24DD and CIO-DD48DD are desig ned for switching circuits of higher
voltage and current than standard TTL type components are capable of. They provide
24 and 48 outputs respectively.
The ‘DD’ designation indicates that these boards are capable of ‘Direct Drive.’ The
current specification that earns the direct drive designation is a switching capacity of
up to 500 mA.
Throughout this manual the part number CIO-DO24DD is used for both products
since most of information applies to both. W here necessary, the appropriate part
number is noted.
Both the CIO-DO24DD and the CIO-DD48DD are s upported by the Universal
Library programming library for DOS and Windows available from Measurement
Computing.
1.1 DIRECT DRIVE
The CIO-DO24DD is similar to a set of non-isolated solid state relays. The digital
lines of the DD are capable of completing a circuit to ground thereby allowing current
to flow in the circuit. Because there is a small amount of OFF current flowing in the
circuit, like a solid state relay, the circuits on a DD board are not ideal for switching
low level signals. If you have a circuit that is suitable for solid state relays and does
not need isolation, the DD board can be substituted.
1.2 DARLINGTON TRANSISTORS
Each output is an NPN Darlington pair. All outputs are open collector and incorporate
clamping diodes for transient suppression. The ability to withstand transients, connect
directly to voltages up to 50V and sink as much as 500 mA make these outputs ideally
suited for controlling lamps, relays, printer hammers and similar loads.
1.3 CLAMPING VOLTAGE
The clamping voltage is th at voltage which, when exceeded, is clam ped to prev ent
damage to th e circuit. The clamping voltage of each 8-bit port can be set
independently and must be supplied externally. In addition, the open collector points
of each 8-bit port can be pulled to a common voltage by connecting an eight-resistor
SIP.
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