SN74LVT245B - what for?

[davemisbehave]

While looking at TIs evaluation module for its THS56X1 series DACs I came across the SN74LVT245B . I (think I) understand what it does, but I'm not sure why it is necessary. Why not just have a direct connection from the DSPs bus to the DACs digital inputs? What would one need bus transceivers for, both in this application and in general?

I have included a picture of the relevant part of the circuit as an attachment. It can also be found on page 24 of the evaluation modules user guide.

THS56X1EVM User's Guide:
http://www.ti.com/lit/ug/slau032c/slau032c.pdf

THS5661A datasheet:
http://www.ti.com/lit/ds/symlink/ths5661a.pdf

SN74LVT245B datasheet:
http://www.ti.com/lit/ds/symlink/sn74lvt245b.pdf

TIA!

[Skimask]

So you can tristate the bus so the bus can do other things while you're not reading/writing to the DAC.
Otherwise, you'd need 16 more dedicated lines just for the DAC.

[davemisbehave]

Thanks, it all makes sense now!

[SeanB]

Another common use for bus drivers on a DAC is to isolate the DAC inputs from the bus so that the data from the other MCU activity on the input will not show up as noise on the output. Often used on higher resolution devices, along with having a separate dedicated digital supply for the bus driver, just to get the noise figure closer to the thermal noise of the DAC and reference. Adds an extra gate delay, and needs a separate enable pin to drive it from the address decode logic, but gives a stable data drive to the DAC latches.