68300

Hi everyone!
	2 years ago,I had asked Charles Melear many questions about MC683332 through the mailing list.
But later the mailing list dispeared.Today I finally find it in YAHOO.This is the first time I 
come here.Several days ago,I asked Charles Melear some question,I write the question and his answers
here,maybe it is useful to you.

>	1.CPU is also MC68332,but has many 8bit width interface IC (8 or 10 CAN,ARCNET controllers),
>I always connect 8bit interface to D8-D15 of 68332,this time I wonder can 68332 drive so many
>IC? Do I need to add buffers(such as 74HC245)?How can I do? I think maybe I can connect half
>of the controllers to D0-D7 of 68332,doing so maybe I can decrease the burden of 68332?

Liubo,

How many devices are you planning on connecting to the data bus?  

You can connect peripherals to both the upper half and lower half of the data bus although it presents nightmares for your software guys.  Basically you have to configure the bus as a 16 bit bus and then read the bus as a 16-bit value and mask off the portion that you do not want.  The other problem is that you have to address the buss as consecutive words as opposed to consecutive bytes.  That is, there is no address 0 line.  You might be able to use the MOVEP instruction.  I have never used it but I think it is supposed to facilitate what you are suggesting.

>	2. I use 68332 at 25M clk,do I need to select a high speed memory chip?Is it enough
>if I use 70ns speed chip?

Liubo,

I believe that the minimum access time is two full S-clock cycles.  The S-clock is essentially equal to the internal bus speed.  I have not gone through the calculations but I believe that you actually need 80 ns. memory to run with no wait states at 25 MHZ  (40 ns period).  Anyway, 70 ns would do.

>	3.In my system,I use SPI to connect to other IO boards.In the last design,I find that some
>time it is abnormal when I use SPI(input or output error),I think the first reason is I choose
>the high speed SPI,but the main reason is 68332 SPI drive many SPI device and there are distances
>about 50CM to 68332.Can I improve the quality of SPI by add buffers(74245) at each IO boards?
>Can I do other things?

Liubo,

I am not sure what to tell you here.  50 cm doesn't sound like too long a wire that it is going to give you problems.  You have to use decent wire and maybe even shielded wire.  Buffers on the SPI are used all the time.

>	Thank you very much!	
 
           liubo
            boliu@...