IBM 1 Series - Digital Output (DO); Integrated Digital I;O Operational Characteristics; Digital Output Operation

Digital Output (DO)
The integrated digital I/O feature has two groups of digital output. Each
DO group has:
e User-output points (16). Each point provides a nonisolated, solid-state
current switch or TTL (transistor-transistor logic) compatible output
voltage.
« One 16-position DO data register.
e An ‘external sync’ input line and a ‘ready’ output line.
e Interrupt capability from the ‘external sync’ input line.
Each digital output group has a unique device address and responds to
specific commands. Data is stored into the DO data register by the Write
DO command. The DO data register is reset only by a power-on reset.
A DO group can be tested using three special commands: Disable DO,
Read DO, and Set Diagnostic External Sync. The Disable DO command
disables the user outputs. The Read DO command reads the contents of
the DO data register. The Set Diagnostic External Sync command disables
the user outputs and simulates the user’s ‘external sync’ line.
DO External Sync
DO external sync consists of two signal lines: an ‘external sync’ input line
and a ‘ready’ output line. A DO group is set to external sync mode by
execution of the Arm DO External Sync command. When a Write DO
command is executed in external sync mode and the data on the DO
output is good, an active level on the ‘external sync’ input line causes the
‘ready’ line to become active. The user signifies receipt of the data by
deactivating the ‘external sync’ line. An interrupt is then posted and the
‘ready’ line becomes inactive. The ‘ready’ line stays inactive until another
Write DO command is executed and ‘external sync’ becomes active again.
The ‘external sync’ line must perform another transition from the 1-state
to the O-state to cause another interrupt.
External sync mode is reset by a Device Reset command, a Halt I/O
command, or any reset condition.
Integrated Digital I/O Operational Characteristics
The timing charts in this section show a logical 1 as a down level (typically
0 Vdc), and a logical O as an up level (typically +5 Vdc).
Digital Output Operation
Each DO group can operate in one of three modes: non-interrupting,
external sync, and diagnostic.
Non-Interrupting Mode
When operating in the non-interrupting mode, each 16-point DO group is
controlled with a Write DO command. A logical 1 written to a point turns
the output transistor on. The output remains in that condition until the
next Write DO command is executed. The contents of the DO register may
be read using the Read DO command without changing the state of the
output drivers.
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