On Sat, Feb 12, 2011 at 12:01 AM, Lyos Gemini Norezel <
[email protected]> wrote:
> On 02/12/2011 02:33 AM, Oliver Seitz wrote:
>
>> Yes, but they really select chips, not drives. They select different PATA
>> register sets on the drive.
>>
>
> I see.
>
>
> USART ("RS232") can be used, of course. As it is only internal
>> communication, you're free to choose any baud rate. You can configure a
>> 16F877@20MHz to communicate at 5 megabaud, I think.
>
>
1.2Mbps with a lot of struggle.
Vasile
> You can not however translate this to RS232 levels using a MAX232, but you
>> don't have to. Just connect the TX line of one PIC to the RX line of
>> another.
>>
>> SPI does not need start and stop bits, so the usable data rate can be
>> slightly higher, but you need more pins. And, SPI supports chip-select
>> inputs or daisy-chain setup, so multi-device-communication is easier with
>> SPI.
>>
>
> Interesting... 5Mbaud over RS232 pins?
> I didn't think RS232 could allow for such speeds... given the hazards of
> crosstalk, etc.
>
> The daisy-chain setup is quite useful in a serial bus... what's the
> theoretical limit with PIC SPI?
> 128 devices per bus? or is it higher than that?
>
>
>
> How do you count four? PATA only supports Master and Slave, that makes two
>> drives per controller.
>>
>> You can multiplex the PATA connectors using bus drivers, like 74HC245. If
>> you're only using one drive at a time, that could be a cheap and simple
>> solution. You can easily expand one controller to 20 hard drives this way.
>>
>
> Given the number of IOs on a 40 pin PIC like the two I have... getting 4
> drives per PIC isn't exactly a magic trick.
>
> The data bus remains the same for the two buses (hence 4 drives)... as well
> as some of the control lines.
> The remaining lines that differentiate drives would have their own IO pins
> still remaining within the IO limit of a 40 pin PIC.
>
> The original schematic (here:
> http://justanotherlanguage.org/sites/default/files/pata_hard_disk_schematic.jpg)
> only used 16 data pins, and 5 control lines! To add a second "bus"... all
> you'd need is another 5 control pins
> (if you need all 5 separate), which is very easy given the left over
> real-estate of the original schematic.
>
> You certainly don't need a bus driver to handle a measly 4 PATA drives.
>
> Either way... using bus drivers or not... you can only access 1 drive at a
> time.
>
> More than sufficient for a media player project.
>
> Lyos Gemini Norezel
>
>
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