Data Translation DT340, Getting Started Manual

Page: 26 / 70

Chapter 3
18
If you are using high-frequency external clock input signals (greater
than 1 MHz), perform the following steps:
1. Insert a resistor to ground for the corresponding counter/timer
clock input signal on the DT340 board. This resistor is used in
parallel with the 1 k
Ω
resistor on the board. The appropriate
value for the user-supplied resistor depends on your application,
the frequency of the clock input signal, and the cable length.
Note: When using clock sources greater than 1 MHz, it is
recommended that you use counter/timers 0 to 3. This is the CE
configuration of the board.
2. Terminate the corresponding signal on the STP340 panel by
replacing the 0
Ω
resistor on the STP340 with a resistor of an
appropriate matching value ( See “Configuring the STP340” on
page 28. for more information).
For example, if you are connecting an external clock signal to clock
input signal 0 on the DT340 board and running the board at its
maximum clock input frequency, it is recommended that you insert a
110
Ω
resistor to ground on the board for the clock input signal 0, and
replace the 0
Ω
resistor in location R1 on the STP340 panel with a
100
Ω
resistor for proper termination.
Clock Input 5 R6
Clock Input 6 R7
Clock Input 7 R8
Table 2: Clock Input Signals and Resistor Use (cont.)
Clock Input Signal Resistor