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3-16
Setup and Installation
D/A Output Channel Update (DAS-8/AO Only)
Switch S5 determines whether the two D/A outputs will be updated
independently (NORM) or simultaneously (SIM). Independent updates
are the normal mode, while simultaneous updates facilitate
synchronization. Refer to Figure 3-4.
Wait-State Setting (DAS-8/AO Only)
Jumper J3 allows the board to be set for a Wait State. A wait state may be
required when the board is used in computers whose bus speeds are
greater than 8MHz. Placing the jumper on the OFF side disables the wait
state. Refer to Figure 3-4.
Clock Select (DAS-8/LT Only)
Jumper J3 sets the board for the 1.000MHz (internal) or PC system
(external) clock. Refer to Figure 3-2.
Clock
The input to the counter/timers used for A/D timing varies. The DAS-8
uses the PC bus clock while the DAS8-PGA and DAS-8/AO have an
on-board 1MHz crystal oscillator. The frequency of the PC bus may be
determined automatically as described below.
Custom Clock Frequencies
For timing, the DAS-8 Series uses the clock signal on the PC I/O bus or
an on-board crystal oscillator. While the original IBM PC XT and
compatibles always had a 2.384MHz bus clock, ISA Nd EISA bus
machines have no accepted standard for PC bus clock. On many
machines, the clock frequency is one-half the CPU clock frequency
while, on others, it is adjustable using motherboard jumpers or advanced
BIOS setup options. Few manufacturers provide this information in their
documentation. This frequency, however, can by measured by
DriverLINX using the 82C54 timer/counters on the DAS-8.
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