IBM Series 1 User Manual page 160

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Digital
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The integrated digital I/O featu~e has two groups of digital
input/p~ocess inte~~upt.
Each group of digital input has:
• 16 user-input points that sense the value of
non-isolated voltage input.
• One 16-position 01 data register for reading unlatched
data.
• One 16-position PI data register
fo~
reading latched
data.
• An "external sync" input line and a "ready" output
line.
• Interrupt capability from either external sync or
process interrupt.
Each digital input group has a unique device address and
responds to specific commands. Addressing and commands are
discussed in the prerequisite publications listed in the
Preface of this manual. The data registers and the
functions performed
by
Dr/PI are described in the remainder
of this section.
Each position of the D1 data register follows the state of
the corresponding user-input point until the register is
read. The data in the register is held (1) during a read
command or (2) when the external sync input becomes active
while in external sync mode. In the second case, the data
~emains held until the resulting interrupt is serviced and
th€ ready line is activated. For additional information,
see "DI External sync
fl
in a subsequent part of this chapter.
Each position of the PI data register records, with a 1-bit,
the first Q-bit to 1-bit transition ou the corresponding
user-input point. The data in the register remains until
reset by one of the following:
1. Read PI with Reset command
2. Arm PI command
3. Device Reset command
4. System reset
5. Power-on reset
When a bit in the PI data register becomes active, a process
interrupt is generated if PI mode was previously set with an
Arm PI command. For additional information, see "Process
Interrupt.
1t
A
Dr/PI
group can he tested using two special commands: (1)
Set Test Ones and (2) Set Test Zeros. When the appropriate
command is executed, the user inputs are disabled, either
ones or zeros are placed on the input receivers, and the
external sync receiver is pulsed. Then when subsequent read
commands are issued, the group responds exactly as if the
actual user inputs had been set, including the PI and
external sync functions.
Integrated Digital I/O 5-3