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When manual update is in effect, the reset field appears
on the screen only after you select the start field. When
auto update is in effect, the reset field always appears on
the screen. This is because even after IDAV is sent or
when you select reset to discontinue waiting, the Digital
Input will now wait for the next IDAV to be sent.
When the Digital Input appears in the System View
Window in manual update mode with the handshake
enabled, the letter "W" can appear next to the Digital
Input's label. This letter appears whenever the Digital
Input is waiting for new input data from the external
device. AfteT the Digital Input receives the new data, the
input display is updated and the letter "M" will appear
next to the Digital Input's label.
Figure 3-3 shows the timing relationship between the
Input Data Available (IDAV) signal that must be provided
by the external device, and the Input Data Accepted signal
(IDAC) from the Digital Input.
INPUT DATA
3C
VALID DATA
DON'T
CARE
W//A
CAN CHANCE
AT ANY TIME
(LOW TO HIGH)
Figure 3-3. Input Handshake Timing Diagram
The high-to-low transition of IDAV, (when pulled low by
the external device alerts the Digital Input that data is
available. The input data must be stable before IDAV is
3-8
Manual Instrument Contro
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