ADLINK Technology ACL-7122 User Manual page 30

2. Output Latch
When an output port is programmed as output mode through
control word, it will not affect the connected output device until
an output instruction is executed. This means the data will not
output until execute the first output instruction.
INPUT/OUTPUT Select
Data From
Data Bus
WRITE
To Data Bus
Figure 3.1 ACL-7122's Signal Direction
3. According the above ACL-7122's signal direction block
diagram, some issues should be careful.
a. When a port is set as INPUT or after hardware RESET,
its output buffer is Disabled (high impedance)
b. The output data is lactated in the Output Latch when it is
set as OUTPUT mode.
c. When the port is set as OUTPUT, the input circuit is
used as an output status read-back.
d. The data in Output Latch is an random value after power
on. It has to be initialized before the port to output
direction.
Output
Latch
READ
Output
Buffer
Input
Buffer
Digital I/O Programming • 21
External Device