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DACKl
DACK3
Fig. 1-5 - DMA Acknowledge ChannelJumper, P6
YI -8254 Timer/Counter Clock Sources (Factory Settings: CLKI-XTAL, CLK2-OTI, PCK)
This header connector, shown in Figure l-6, lets you select the clock sources for the 8254 timerlcounters, TC0,
TCl, and TC2. TCO and TCI are cascaded to form the pacer clock. You must install two or three jumpers in order to
properly use the timer/counter features, including the pacer clock. Figure l-7 shows a block diagram of the timer/
counter circuitry to help you in making these connections.
The clock source for TCO and TCI is selected by placing a jumper on XTAL or ECI on CLK1 (the two pairs of
pins at the top of the header). XTAL is the on-board 8-MIIZ clock and ECI is an external clock source you connect
through the external I/O connector e245).
Below the CLKI pins are three pairs of pins labeled CLK2. These pins are used to select the clock source for
TC2. OTI connects the output of TCI to the clock input of TC2. Installing a jumper here cascades all three timer/
counters, a feature necessary when using SIGNAL*MATH or ATLANTIS application software (see Appendixes D
and E). XTAL is the on-board 8 MHz clock, and EC2 is connected to the same external clock source as ECI
(n4r.
The last two pins on this header, PCK and ET, let you use the pacer clock (PCK) or an external trigger (ET) to
trigger AID conversions. A jumper must be placed on PCK in order to use the pacer clock (output from TCI). Or,
you can place the jumper across ET and connect any external trigger toY2-39 to trigger the A/D converter.
NOTES: You must disconnect the pacer clock by removing the PCK jumper and install the jumper of ET
whenever you use the external trigger line. You must have one jumper installed on one of the npo CLKI selections
and one jumper installed on one of the three CLK2 selections.
tr
P 6
Y
o
(\|
Y
o
P7
IH
XTAL
EC1
oTl
XTAL
EC2
PCK
ET
Fig. 1-6 -8254 Timer/Counter
Clock Source Jumpers, p7
l-5
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