EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Simbarashe Bryne Chipembe on June 26, 2015, 03:36:40 pm
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Hi guys I am trying to use the SN74abt16623, question is I don't understand how you make it store or "latch" data. eg latch A data on b bus and keep it there, even when A data changes ( not transparent)
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Read page 1 of the datasheet, which says...
"The dual-enable configuration gives the transceivers the capability of storing data by simultaneously enabling OEAB and OEBA. Each output reinforces its input in this configuration."
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According to this description in the datasheet:
The dual-enable configuration gives the
transceivers the capability of storing data by
simultaneously enabling OEAB and OEBA. Each
output reinforces its input in this configuration.
When both OEAB and OEBA are enabled and all
other data sources to the two sets of bus lines are
at high impedance, both sets of bus lines (32 total)
remain at their last states.
It sounds like they can only latch data from their own busses, and only do it simultaneously.
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Storage is explained in the second paragraph of the first page of the datasheet http://www.ti.com/lit/ds/scbs211b/scbs211b.pdf (http://www.ti.com/lit/ds/scbs211b/scbs211b.pdf)
Have your external circuit drive one side or the other to the value you want to store, then assert both output enables (OEAB high and /OEBA low). Then you can tri-state your external circuit, and the transceiver will hold the value.
You end up with two devices driving the bus in between asserting the output enables and tri-stating your driver, but that's OK as both will be driving the same value.
What it can't do is store data while the bus on either side is driven to different values ("even when A data changes"). That will make either it, your other driver, or most likely both, very unhappy.
A small CPLD might be your best option, if you need it bidirectional and able to store data while the input side changes.