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Chris hasn't responded to a query yet, but it appears that the BX-24p T1
pin (ATmega8535 processor pin 41) is available. It is used on the BX-24
for ATN, but the BX-24p has moved ATN to the Reset pin. This permits
using T1 to increment Timer1 from an external source, in my case,
freeing the interrupt system which I've been using to count irregular
pulses at ~720Hz.

I've tied T1 to BX-24p pin 9 for physical convenience and the
opportunity to examine the input in code, but it can be brought off the
module with a flying lead, of course. Timer1's current count can be
read and reset in code and its compare registers can be used to signal
or act upon desired threshold counts.

On both the BX-24 and BX-24p, pin T0 (processor pin 40) is also free and
can be used for an external RTC tick source or to synchronize BX-24s.
See http://groups.yahoo.com/group/basicx/message/11090 and thread. Tom
//





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Tom,

> Chris hasn't responded to a query yet, but it appears that the BX-24p T1
> pin (ATmega8535 processor pin 41) is available. It is used on the BX-24
> for ATN, but the BX-24p has moved ATN to the Reset pin. This permits
> using T1 to increment Timer1 from an external source...

This confirms something I have suspected.

> I've tied T1 to BX-24p pin 9 for physical convenience and the
> opportunity to examine the input in code, but it can be brought off the
> module with a flying lead, of course. Timer1's current count can be
> read and reset in code and its compare registers can be used to signal
> or act upon desired threshold counts.

The BX-24p has very constrained packaging which doesn't do justice to
the power of the chip. I avoid all of these difficulties by using a
BX-35 where I can access any pin I like. Yes it takes up more room but
its worth it and cheaper too even with the support chips.

Luckily my BX-35/AVR Development Board already has a jumper for ATN/T1
input to pin 2 of the BX-35 PDIP. One day I should publish the schematic :)

Mike
http://home.austin.rr.com/perks/basicx/




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More:

BX-24p T1 works fine and, when used with ICP (pin 12) and INT1 (pin 11)
to capture and signal an index, and using Timer1's CompareA register to
reset the counter at a max count, a high-speed indexed modulo axis
counter is easy.

A fast axis tick, via T1, clocks Timer1 up (it can also decrement) until
the CompareA count resets it, modulo n. An axis event (an index) pulse
both causes an immediate count latch to Input Capture registers ICR1H
and ICR1L, and requests an interrupt. Since the event count is latched,
despite interrupt latency, the true count at the moment of the index is
available in the Capture registers, and no semaphore is necessary to
access those registers since they are never changed by code, only by
hardware. And it can be very fast; T1 can be clocked at the processor
crystal frequency.

I'm happy, and the processor can think again. Tom





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Wow another BXer in OKC im amazed Greg, this is a breakthrough...JK,
im in OKC as well 63rd and portland..you? I thought i was alone here
everyone else ive known here uses BS2. You a electronics hobbiest or
practitioner? Im currently a junior EET major at OSU. not much time
for the bx anymore we use pics in our program but someday i will have
time to build again! hey just thought i would give a fellow okie a
shout!

Daniel





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