Advantech MIC-3756, Manual

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4.3 Channel-Freeze Function
The MIC-3756 provides the Channel-Freeze function for isolated
digital output channels. When Channel-Freeze function is enabled, all
ports on the card will be locked so that the data transmi tted (from the
host PC) to the card won’t be transferred to the DO ports. Once the
Channel-Freeze function is enabled, each port status is immediately
frozen into its last valid value before the Channel-Freeze . Since the
value transmitted (from the host PC) to the card is also stored in the
buffer on the PC, thus when users call the DRV_DioGet
CurrentDOByte ( ) function to read back the DO channel value, this
function will determine that:
If Channel-Freeze function is disabled, it will return the DO value on
the port;
If Channel-Freeze function is enabled, it will return the value from the
buffers on host PC.
The MIC-3756 provides digital input channel (CH_FRZ_IN) to enable
channel-freeze function. The channel-freeze function acts when the
pin CH_FRZ_IN is activated. Moreover, you can setup the input mode
of channel-freeze function input channel CH_FRZ_IN as dry contact
input mode or wet contact input mode selected by on-board jumper
JP2, as shown in Table 4-8 . The wiring in wet contact and dry contact
input mode are shown in Fig. 4 -2 . Otherwise, you also can enable the
function through software by writing “1” to CFC (Channel-Freeze
Function Control) bit on channel-freeze function register, as shown in
Table 4-9 and Table 4-10 . It’s useful in software simulation and