Manual Number: 00650-014-4
Page 4-4
AD12-8 Manual
Base + 0 Write:
Write digital output.
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%
%
%
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%
'2
'2
'2
'2
'2
'2
'2
'2
DO0-DO7:
These are digital outputs if so programmed by jumpers D0-D7.
Base + 3 Read:
Read digital input.
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%
',
',
',
',
',
',
',
',
DI0-DI7:
These are digital inputs if so programmed by jumpers DO-D7.
Counter/Timer Registers
Base + 4 Write/Read:
Counter #0 read or write. When writing, this register is used to load a
counter value into the counter. The transfer is either a single or double byte transfer, depending on
the control byte written to the counter control register at BASE A 7. If a double byte
transfer is used, then the least-significant byte of the 16 bit value is written first, followed by the
most significant byte. When reading, the current count of the counter is read. The type of transfer
is also set by the control byte.
Additional information about the type 8253 counters is presented in
CHAPTER 8: PROGRAM-
MABLE INTERVAL TIMER
section of this manual. However, for a full description of features
of this extremely versatile IC, refer to the Intel 8253 data sheet.
Base + 5 Write/Read:
Counter #1 read or write. See description for
Base + 4
Write/Read
.
Base + 6 Write/Read:
Counter #2 read or write. See description for
Base + 4
Write/Read
.
Base + 7 Write:
The counters are programmed by writing a control byte into a counter control
register at BASE A 7. The control byte specifies the counter to be programmed, the
counter mode, the type of read/write operation, and the modulus. The control byte format is as
follows:
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6&
6&
5: 5:
0
0
0
%&'
