Kinetis "K70" External Bus Interface

[ek_adv]

I noticed that Kinetis "K70" provides 32 address lines for External Bus Interface but maximum addressable memory size is 256MB which is requiring 26 lines. Is there any reason that this processor has 32 address lines even though you cannot address more than 256 MB?

[xiangjun_rong]

Hi, Eddie,

The 256MB needs 28 address lines(2**(28)=256M), I have checked the section 10.3.1 K70 Signal Multiplexing and Pin Assignments in reference manual of K70, all 32 address lines are available for K70, there are FB_AD0~FB_AD31, you can use a latch such as 74HC573 to latch the address bus with FB_ALE signal so that you can get all 31 address lines. There are also independent address lines of FlexBUS, you can use or do not use them, it is okay to use the latched address bus.

Pls refer to section 4.2 System memory map, the FlexBUS space can be located in the following space: 0xA000_0000–0xDFFF_FFFF, I think you can use the space.

Hope it can help you.

BR

XiangJun Rong