VXI VT1422A - Manual (Page 120)

118 Programming the VT1422A for Data Acquisition and Control Chapter 4
Setting Up Digital Input and Output Channels
Setting Up Digital
Inputs
Digital inputs can be configured for polarity and, depending on the SCP
model, a selection of input functions as well. The following discussion will
explain which functions are available with a particular Digital I/O SCP model.
Setting a digital channel’s input function is what defines it as an input channel.
Setting Input Polarity
To specify the input polarity (logical sense) for digital channels use the
command INPut:POLarity <mode>,(@<ch_list>). This capability is available
on all digital SCP models. This setting is valid even while the specified
channel is not an input channel. If and when the channel is configured for
input (an input FUNCtion command), the setting will be in effect.
•
The <mode> parameter can be either NORMal or INVerted. When set
to NORM, an input channel with 3 V applied will return a logical "1."
When set to INV, a channel with 3 V applied will return a logic "0."
•
The <ch_list> parameter specifies the channels to configure.
The VT1533A has 2 channels of 8 bits each. All 8 bits in a channel
take on the configuration specified for the channel. The VT1534A has
8 I/O bits that are individually configured as channels.
To configure the lower 8 bit channel of a VT1533A for inverted polarity:
INP:POLARITY INV,(@108)
SCP in SCP position 1
To configure the lower 4 bits of a VT1534A for inverted polarity:
INP:POL INV,(@132:135)
SCP in SCP position 4
Setting Input Function
The VT1533A Digital I/O SCP and the VT1534A Frequency/Totalizer SCP
can both input static digital states. The VT1534A Frequency/Totalizer SCP
can also input frequency measurements and totalize the occurrence of
positive or negative edges.
Static State (CONDition) Function
To configure digital channels to input static states, use the
[SENSe:]FUNCtion:CONDition (@<ch_list>) command. Examples:
To set the lower 8 bit channel of a VT1533A in SCP position 4 to input
SENS:FUNC:COND (@132)
To set the upper 4 channels (bits) of a VT1534A in SCP pos 2 to input states
SENS:FUNC:COND (@120:123)