6
Configuring the Equivalent Loads
As shipped, there are two resistor packs installed in sockets J2 and J3. These provide 10
additional equivalent loads, as defined in the IEEE 488.1-1987 standard. For systems with
few devices and long cable lengths, the additional loads provide increased signal
integrity and better transfer rates on the cable. In most situations, they can be left
installed, which gives a total of 11 loads for the card.
However, there is a maximum of 20 equivalent loads per bus system. Most devices
have one equivalent load, so a maximum of nine additional devices can be used while
the resistors are installed. If your bus system will have more than nine additional
devices, carefully remove both of the resistor packs and store them.
If the resistors need to be reinstalled later on, be sure that the visual key aligns with pin
1 on the sockets. The two resistor packs are equivalent, and can be interchanged. Both
resistor packs must be installed together.
For full details on the constraints in configuring a bus system, refer to section 5.2.3 in
the IEEE 488.1-1987 specification. The TAMS card is capable of operation at
1,000,000 bytes per second, and therefore the constraints in that section apply. This
requires 48 mA tri-state drivers be used in all devices, all devices must be powered on,
and cabling must be a maximum of 15 meters total length with at least one equivalent
load per meter of cabling.
