MK66 : Is it possible to use the FB_CSx signal instead of FB_ALE for recognizing a bus transaction start ?

[koichisakagami]

Dear community,
    I have been developing my product with MK66FX1M0VLQ18.

I plan to use the 32bit data bus SRAM with Flexbus.
I hope to use some FB_CSx signals.

But, I think that I can use only FB_CS0 signal.
I can not use the FB_CS1 ,as the FB_CS1 is multiplexed with FB_ALE.

[Question]
    So,Is it possible to use the FB_CSx signal instead of FB_ALE function for recognizing a bus transaction start ?
    If yes,
    an external device can be connected with FB_CSx signal for recognizing a bus transaction start instead of FB_ALE.
    And I can use FB_CS1 signal for chip select function.

Best Regards,
Koichi Sakagami

[koichisakagami]

Dear Xiangjun,

Thank you for your advice.

I got it.

Best Regards

Koichi Sakagami

[xiangjun_rong]

Hi, Koichi,

Regarding your question, I have to clarify the function of FB_CS and FB_ALE. The FB_CSx is used to connect to the chip select pin of SRAM, the FB_ALE is used to latch the address with latch chip. As you know that the K66 has only FB_A29~24 nonmultiplexed address, if you want to accesss external SRAM, you have to use latch chip for example 74LS373 to latch the address in address pahse of bus timing, so the FB_ALE is required to access SRAM with 32 bits data bus.

FB_CS2/FB_CS3/FB_CS4/FB_CS5 are multiplexed with FB_BEx, and FB_CS1 is multiplexed with FB_ALE, so as you said that only FB_CS0 can be used.

I think you can use the connection.

1)use 4 74LS373 and FB_ALE to latch the 32 bits address and connect them to addrss of SRAM, note that you should connect latched address A2 to A0 pin of 32 bits SRAM for 32 bits datya bus access.

latched A2   to A0 of SRAM

latched A3  to  A1 of SRAM

latched A4 to A2 of SRAM

.....................

2)use FB_CS0 to /CS of SRAM

3)connect FB_AD31~0 to data bus of SRAM.

4)conneche FB_OE and FB_R/W to OE and WR pin of SRAM

5)connect the FB_BEx to Byte enable of SRAM.

it is okay.

Hope it can help you

BR

Xiangjun Rong