[En-Nut-Discussion] RTL8019 addressing

[Göran Risén]

Can anyone tell me how the chip select for the rtl8019 works. For instance, 
In the Ethernut 1.3 rev G board, line A15 from the microcontroller is used 
in such a way that it is inverted to the SA15 address line on the ethernet 
device. But I don't understand how this can shut off the rtl ? As long as 
address line 15 is 0, both the external RAM and rtl8019 should be addressed, 
how come there's no collision when both RAM and rtl talks at the same time?

I understand the case when A15 is still 1 and the address is at 0x8000 or 
more. Then the RAM is deselected and the address is moved forward to the 
next device, and only one device is addressed. But is not both devices 
addressed under 0x8000 ?


What is the principle behind all of this? I have seen schematics where only 
the SA0-SA4, SD0-SD7 and control lines are implemented and in this case it 
seems to be a prerequisite to hardwire SA8 and SA9 to Vcc. What would be the 
chip select for rtl in this case, if any?


Göran

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