8254 Programmable Interval Time
••
77
•
M2, M1 & M0 - Select Operating Mode (Bit 3, Bit 2, & Bit 1)
M2
M1
M0
MODE
0
0
0
0
0
0
1
1
x
1
0
2
x
1
1
3
1
0
0
4
1
0
1
5
•
BCD - Select Binary/BCD Counting (Bit 0)
0
BINARY COUNTER 16-BITS
1
BINARY CODED DECIMAL (BCD) COUNTER (4
DECADES)
Note:
1.
The count of the binary counter is from 0 up to 65,535.
2.
The count of the BCD counter is from 0 up to 99,999.
A.3 Mode Definition
In 8254, there are six different operating modes can be selected.
The they are :
•
Mode 0
: interrupt on terminal count
The output will be initially low after the mode set operation.
After the count is loaded into the selected count register, the
output will remain low and the counter will count. When
terminal count is reached, the output will go high and remain
high until the selected count register is reloaded with the
mode or a new count is loaded. The counter continues to
decrement after terminal count has been reached.
Содержание cPCI-7200
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