Hello!
I have to connect a Bus Transceiver to the C6424 EMIFA dada bus in asyncronious mode.
The 74HC245 Bus Transceiver have 2 control pins: OEn and DIR.
The EMIFA have the next control pins: EM_CSn, EM_OEn, EM_WEn and EM_RNW.
I can see the correct way to connect these devices with external glue logic:
DIR = EM_RNW
OEn = (EM_CSn OR EM_OEn) AND (EM_CSn OR EM_WEn)
This method is correct because timing diagram of the transceiver matches exactly as if the bus was connected to an external asynchronous memory, but we have two extra logic gates and time delay.
Can I connect the bus transceiver without the glue logic?
This way:
DIR = EM_RNW
OEn = EM_CSn
The difference is that the bus transceiver will be active the whole read or write cycle, not only when EM_OEn or EM_WEn are active.
I have not found in the documentation that the data bus of EMIFA is tri-stated when the EM_CSn is not active.
If the data bus is not tri-stated when the EM_CSn is not active, we will have the short bus conflict at the moment of the EM_CSn signal switching.
Thanks for any advice!
Serg.
