When to use Buffers for devices connected to Address and Data Bus

I am working with 80c196kc; I have connect 7 to 8 chips to the address and data bus of the microcontroller, including two RAMS(AS7c256) and 6 latches(74hc373).

Question is, should i be using a buffer(74hc245).

Moreover as a rule of thumb how many chips can be safely connected to a buffer/tranceiver.

I have tried using datasheets; the datasheet of latch(74hc373 ) shows a max input current of 20ma and upto 10uA of input leakage current. Whereas the output current of buffer(74hc245) is 20mA. Now i know i cant use the max input current of latch but can i use the leakage current. I am preplexed. Therefore a rule of thumb will be more than welcome.

Reply to
arslan
Loading thread data ...

d

depends on bus speed, bus length, are you having problems? You may need address buffers as well.

Reply to
cbarn24050

Something wrong there - the 20mA must be supply current ?. For ttl, iirc, logic low drive current should be no more than 1.6mA, with logic high in the uA range. 74HC has cmos inputs and should be much lower worst case. Check the data sheet again and perhaps a second one for comparison ?.

Buffers aren't such abad idea though, even if you think you don't need them. Helps to keep the timing tight and edges straight. There's nothing clever about saving the last few possible pennies and the design failing at Vcc or temperature limits...

Chris

Reply to
ChrisQ

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.