Technical information

OPTO DIO Reference Read This First.
The sink driver output schematic is shown in Figure 1-8.
Typical output connections are shown in Figure 1-9. Note only
the pull down scheme works with sink drivers.
The sink drivers can only pull down the output lines.
Sink Driver Output Logical Levels._______________________________
The sink cards are normally fitted with inverting buffer
chips, 74LS540, so that a logical one written to the output
register drives the output high and a logical zero written to the
output port drives the output low. Thus in this normal mode of
operation the voltage level of the output line follows the logic
level in the output register.
The sink cards can be fitted with non inverting buffer
chips, 74LS541, so that a logical one written to the output
register drives the output low and a logical zero written to the
output port drives the output high. See Figure 1-10. Thus in this
inverse mode of operation the voltage level of the output line
does the opposite of the logic level in the output register.
Note since the sink driver chips are inverting and the
source are not the non inverting buffer chips are must be
changed when source and sink drivers are changed.
Figure 1-10. Logically Inverting The Sink Output.___________________________________________
DRIVER BUFFER PORT DATA PORT OPERATION
USED SETTING LINES
SINK 74LS540 INVERTERS 0 = low OFF = low NORMAL
SINK 74LS540 INVERTERS 1 =high ON =high NORMAL
SINK 74LS541 0 = low ON =high INVERSE
SINK 74LS541 1 =high OFF = low INVERSE
Note: By default Sink driver, since they are inverting drivers
themselves, use 74LS540 inverting buffers to give a non inverting
output. Using 74LS541 buffers will invert the output signals.
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