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Publication No. 980855 Rev. A
General
Digital Module
Ports
Asynchronous
Digital Operation
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Digital Module Operation
The 1256 may be used to control the 1260-114TTL, 1260-
114CMOS, 1260-114OC, and 1260-114HVOC digital modules.
These modules may be programmed to work in either the
synchronous or asynchronous modes of operation. The
modules may be programmed to operate in a combination of the
two modes, with some ports operating in the asynchronous mode
and some ports operating in the synchronous mode.
The 1260-114 modules are programmed at the "port" level. A port
is a set of 8 consecutive input/output pins. Data is written to the
ports in 8-bit bytes. The 1260-114TTL, 1260-114CMOS, and 1260-
114OC modules consist of twelve 8-bit ports, for a total of 96
input/output pins. In the case of the 1260-114HVOC card, it
consists of six 8-bit ports.
For the TTL/CMOS versions of the 1260-114, each port may be
defined as an input or an output. All 8 pins of an output port will be
enabled to output data when the port is enabled. Data may be read
from an output port, but data written to an input port will not appear
on the signal pins.
The open-collector versions of the 1260-114 are generally thought
of as output only modules. If an output bit is turned off (high-
impedance state) such that the 1260-114 is not actively pulling a
signal low, reading the port will return the present signal level. It is
possible, therefore, to determine whether something else is driving
the system and whether the signal is either high or low when
referenced to CMOS levels.
When the 1260-114 modules are programmed to operate in the
asynchronous mode, data is written to the output pins immediately
upon receipt of the DIGITAL:OUTPUT command. Likewise, the
data is read from the input pins immediately upon receipt of the
DIGITAL:INPUT? command.
1256 User Manual
Chapter 7
Digital Module Operation 7-1
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