Multiplexer 3: Delta Tau ICLK input

The ACC-14D parallel input boards to the Delta Tau digital servo control system must be told when new valid inputs are available from the NI PCI-6534 digital output boards. This is accomplished by raising the ICLK inputs on the ACC-14D boards. The source of this signal varies according to scan mode; Multiplexer 3 is used to select between two inputs, and Multiplexer 3's select input is provided by the high bit of Multiplexer 2's select input as follows:

• When the NI PCI-6534 board is driven in external clocking mode such that its REQ1 pin is a trigger input, it raises its ACK1 output as new digital positions become available. We therefore pass the NI PCI-6534 ACK1 output to the ACC-14D ICLK inputs when the Multiplexer 2 select input has its high bit set to zero (an input of $0=00_{2}$ or $1=01_{2}$).
• When the NI PCI-6534 board is driven in internal clocking mode, it raises its REQ1 output as new digital positions become available. We therefore pass the NI PCI-6534 REQ1 output to the ACC-14D ICLK inputs when the Multiplexer 2 select input has its high bit set to one (an input of $2=10_{2}$ or $11_{2}$).

One must also connect the ACC-14D ERR1 and ERR2 inputs to ground.