USB5841 Data Acquisition
MODE 3 Square wave mode
Mode 3 is typically used for Baud rate generation. Mode 3 is similar to Mode 2 except for the duty cycle of OUT. OUT
will initially be high. When half the initial count has expired, OUT goes low for mainder of the count. Mode 3 is
periodic; the sequence above is repeated indefinitely. An initial count of N results in a square wave with a period of N
CLK cycles.
GATE=1 enables counting; GATE=0 disables counting. If GATE goes low while OUT is low, OUT is set high
immediately; no CLK pulse is required. A trigger reloads the Counter with the initial count on the next CLK pulse.
Thus the GATE input can be used to synchronize the Counter
After writing a Control Word and initial count, the Counter will be loaded on the next CLK pulse. This allows the
Counter to be synchronized by software also.
Writing a new count while counting does not affect the current counting sequence. If a trigger is received after writing a
new count but before the end of the current half-cycle of the square wave, the Counter will be loaded with the new
count on the next CLK pulse and counting will continue from the new count. Otherwise, the new counter will be loaded
at the end of the current half-cycle.
Mode 3 is implemented as follows:
Even counts: OUT is initially high. The initial count is loaded on one CLK pulse and then is decremented by two on
succeeding CLK pulses. When the count expires OUT changes value and the Counter is reloaded with the initial count.
The above process is repeated indefinitely.
Odd counts: OUT is initially high. The initial count minus one (an even number) is loaded on one CLK pulse and then
is decremented by two on succeeding CLK pulses. One CLK pulse after the count expires. OUT goes low and the
Counter is reloaded with the initial count minus one. Succeeding CLK pulses decrement the count by two. When the
count expires, OUT goes high again and the Counter is reloaded with the initial count minus one. The above process is
repeated indefinitely. So for odd counts, OUT will be high for (N+1)/2 counts and low for (N-1)/2 counts.
BUY ONLINE at art-control.com/englishs or CALL +86-10-51289836(CN)
14
