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PROGRAMMING INFORMATION
Table 3-9.
PIT Time Intervals Vs. Timer Counts
T
N
10 usec
12
100 usec
123
1 msec
1229
10 msec
12288
50 msec
61440
*Count Values (N) assume clock is 1.23 MHz.
Count Values (N) are in
decimal.
3-14.
8251A PCI PROGRAMMING
The 8251A Programmable Communications Interface (PCI) converts parallel
output data into virtually any series output data format (including IBM
Bi-Sync) for half-or full-duplex operation.
The PCI also converts serial
input data into parallel data format.
Prior to transmitting or receiving data, the PCI must be loaded with a
set of control words.
These control words, which define the complete
functional operation of the PCI, must imediately follow a reset (internal
or external).
The control words include a Mode instruction and Command
instructions.
3-15.
MODE INSTRUCTION FORMAT
The Mode instruction word defines the general characteristics of the PCI
and must follow a reset operation.
Once the Mode instruction word has
been written into the PCI, sync characters or command instructions may be
inserted.
The Mode instruction word defines the following:
a.
For Sync Mode:
( 1) Character length
(2) Parity enable
(3) Even/odd parity generation and check
( 4) External sync detect
(5) Single or double character sync
b.
For Async Mode:
(1) Baud rate factor (X16-X64)
( 2) Character length
3-18
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