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'Newbie 16C6x questions'
1996\12\11@135903 by Matthew Mucker

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After a successful project with the '56, my next project is a little more
ambitious.  I'm planning on using a '63 but have a few questions.

1)  The USART asynchronous mode "uses standard nonreturn to zero )NRZ)
format..."  is this what RS-232 uses?  Can I just hang a MAX232 off the
pins and get an RS-232 port?

2)  What is this whole shebang about two banks of registers?  If I need to
swap the two banks in and out, why do they have different addresses?  I'm
confused.  I mean, portc is at 07h and trisc is at 87h.  They have unique
addresses, why is it necessary to switch banks?  Can't they just be
addressed directly?

Obviously, I'm missing something here...

-Matt


 "DOS Computers manufactured by companies such as IBM, Compaq, Tandy, and
millions of others are by far the most popular, with about 70 million
machines in use wordwide. Macintosh fans, on the other hand, may note that
cockroaches are far more numerous than humans, and that numbers alone do
not denote a higher life form."

1996\12\11@144203 by Norm Cramer

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At 02:06 PM 12/11/96 +0500, you wrote:
>After a successful project with the '56, my next project is a little more
>ambitious.  I'm planning on using a '63 but have a few questions.
>
>1)  The USART asynchronous mode "uses standard nonreturn to zero )NRZ)
>format..."  is this what RS-232 uses?  Can I just hang a MAX232 off the
>pins and get an RS-232 port?

Yes

>
>2)  What is this whole shebang about two banks of registers?  If I need to
>swap the two banks in and out, why do they have different addresses?  I'm
>confused.  I mean, portc is at 07h and trisc is at 87h.  They have unique
>addresses, why is it necessary to switch banks?  Can't they just be
>addressed directly?
>

Well they can be addressed using thier full address INDIRECTLY.  The PIC
instruction format does not allow space for the full 8 bit (or longer)
address of the RAM location.  There are bits in the STATUS register that
"complete" the address.  I think all of the current PIC's only have two
banks and only use RP0 but the architecture allows for RP1 to address two
more banks.

See the databook for more details.

Norm

1996\12\11@163548 by Robert Lunn

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>1)  The USART asynchronous mode "uses standard nonreturn to zero )NRZ)
>format..."  is this what RS-232 uses?  Can I just hang a MAX232 off the
>pins and get an RS-232 port?

       Yes.

>2)  What is this whole shebang about two banks of registers?  If I need to
>swap the two banks in and out, why do they have different addresses?  I'm
>confused.  I mean, portc is at 07h and trisc is at 87h.  They have unique
>addresses, why is it necessary to switch banks?  Can't they just be
>addressed directly?

       Look at the description in the data sheet of, for example, ADDWF.

       You'll see that the instruction includes SEVEN bits to address the
       file register.  That is, it can select one register from 128.

       87h is 135.

       So the ADDWF is unable to address every register from 00h to 87h.

       To overcome this limitation, two EXTRA address bits are stored in
       the status register.  These extra address bits are then prefixed
       to the address bits in the instruction, giving a NINE bit address.
       As you point out, this is now enough to select the register.

       However, you must ensure that the extra address bits in the status
       register are properly set before you execute the instruction, so
       that the desired nine bit address is generated.

___Bob

1996\12\12@122448 by Matthew Mucker

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>>2)  What is this whole shebang about two banks of registers?  If I need to
>>swap the two banks in and out, why do they have different addresses?  I'm
>>confused.  I mean, portc is at 07h and trisc is at 87h.  They have unique
>>addresses, why is it necessary to switch banks?  Can't they just be
>>addressed directly?
>>
>
>Well they can be addressed using thier full address INDIRECTLY.  The PIC
>instruction format does not allow space for the full 8 bit (or longer)
>address of the RAM location.  There are bits in the STATUS register that
>"complete" the address.  I think all of the current PIC's only have two
>banks and only use RP0 but the architecture allows for RP1 to address two
>more banks.
>
>See the databook for more details.


NOW it makes a whole lot more sense.  The databook didn't explain it as
clearly as you just did.  Thanks!

-Matt


 "DOS Computers manufactured by companies such as IBM, Compaq, Tandy, and
millions of others are by far the most popular, with about 70 million
machines in use wordwide. Macintosh fans, on the other hand, may note that
cockroaches are far more numerous than humans, and that numbers alone do
not denote a higher life form."

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