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PROGRAMMING INFORMATION
Table 3-4.
PIT counter Operation Vs. Gate Inputs
Signal
Low
Status
or Going
Rising
High
Modes
Low
0
Disables counting
--
Enables counting
1
--
i)
Initiates counting
--
2)
Resets output
after next clock
2
1)
Disables counting
2)
Sets output
Initiates counting
Enables counting
immediately high
3
1)
Disables counting
2)
Sets output
Initiates counting
Enables counting
immediately high
4
Disables counting
--
Enables counting
5
--
Initiates counting
--
3-7.
ADDRESSING
As listed in Table 3-3, the PIT uses four I/O addresses.
Addresses 0000,
0002, and 0004, respectively, are used in loading and reading the count
in counter 0, 1, and 2.
Address 0006 is used in writing the mode control
word to the desired counter.
3-8.
INITIALIZATION
To initialize the PIT chip, perform the following:
a.
Write a mode control word for counter 0 to 0006.
Note that all mode
control words are written to 0006, since the mode control word must
specify which counter is being programmed.
(Refer to Figure 3-1.)
Table 3-5 provides a sample subroutine for writing mode control words
to all three counters.
3-12
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