Actually, my loader isn't tying up the usart at all.  It only uses it during
load.  Then the system itself can use it after boot to retrieve my logged
data etc...  No response from PC within a few ms means go and boot...

Kyrre

----- Original Message -----
From: "Byron A Jeff" <byron@CC.GATECH.EDU>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Saturday, June 26, 2004 10:40 PM
Subject: Re: [PIC:] 16F88 RS232 bootloader.


> On Sat, Jun 26, 2004 at 12:49:15PM -0400, Victor Faria wrote:
> > Sorry if this is a stupid question??
>
> Why would you think that?
>
> > But with all the talk about bootloaders is it possible to turn these
into a
> > single pin loader???
>
> Of course! Tato's loader is a prime candidate because it bit bangs the
> serial interface.
>
> > Much like Wouter's. Even if it costs some memory but you gain a pin it
may
> > be a good trade off!!
>
> There are more advantages:
>
> 1) You get to pick the I/O pin.
> 2) You don't have to tie up the USART.
> 3) Since it's a bit banged interface you can dynamically adjust the bit
rate
>    so that the load will work using the internal oscillator even when the
temp
>    fluctuates.
>
>
> Wouter's basic idea is sound. A single pin interface is created by tying
the
> RX and TX pins of the serial interface via a resistor (he shows 330 ohms
> on his WLoader schematic here: http://www.voti.nl/wloader). Then the TX
> driver output pin is connected directly to a PIC I/O pin. So the PIC I/O
pin
> can drive TX, receive from RX, with only the minor side effect of
everything
> from RX being echoed to TX, which is actually a good check for the PC side
> loader software.
>
> BTW for bit banging serial Timer 2 is great as a bit rate generator when
it's
> available. With the period register PR2 set, the timer will auto reset
after
> the given interface. So you can set it to time out and auto reset after
one
> bit cell. Then only a single bit needs to be checked to see when to
transmit
> or receive the next bit from the serial interface.
>
> Lastly the single pin interface will cost only a trivial amount of code
over
> a 2 pin bit banged interface. The only difference is that you have to turn
> the TRIS bit for the pin around from transmitting to received. Otherwise
it's
> exactly the same. So 2 instructions to save an I/O pin, especially on an
18
> pin part? Definitely a winner.
>
> BAJ
>
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