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'[PIC]: 8bit Data bus using a PIC16F84A.. A dream o'
2001\05\29@101358 by Dylan Hillier

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>sure it has enough pins ya just gotta use a 688 as a address comparator and
>an 8 bit bus latch :-)

Im new to all this stuff... i know phillips makes such a device (668
comapator) but i can never find a IC packaged 8 bit bus latch. Is there
such a thing or will i have to to make one from 8 d-flip-flops in parallel
with a common clock input and a tri-state enable input?

Hrrmmm.. i thought u could use the 8 pins of PortB as the databus, 3 pins
of port A as the address bus (giving up to 8 devices ?), then use the
remaining 2 pins(Control Bus) of port A as I/O Read/Write.  Then all u need
would be an address decoder IC and a set of tristate latches (input/output
latch) for each device (up to 8) for each device you plug onto the open
collector type bus?

Keep in mind i have no idea what im doing.. im working off some pretty
strong assumptions here and i have no experience at all with pic's other
than writing simple software and controlling LCD (which i finally got to
work after 3 long hard weeks of pulling my hair out.)

Someone mentioned memory mapped I/O, how does this differ from my above
mentioned scheme, does it mean there is a huge chunk of memory, and instead
of each device being on a bus it just writes to its own hard coded (in my
case) memory address, then the pic poles the addresses for device changes?

This is all getting interesting..





>andrew -- i was gonna make a isa programmer but i shelved it
>{Original Message removed}

2001\05\29@141907 by Andy N1YEW

picon face
74LS688 :-)

i have a slight idea of what i am doing as i researched it.....

the 74LS245 is used as a bus latch.

later
andy  -- i used have no clue what i was doing.  now i have a clue what i am
NOT doing ;)
{Original Message removed}

2001\05\29@145225 by ael E Maj ACC/XPPI

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I'm venturing out on a limb here but I don't believe the 245 is a latch...it
is only a bi-directional buffer.  Like its brother the 244 which is only one
way, with its inputs on both side on the chip to ensure a messy layout.
Note:  I would always use a 245 en lieu of a 244 and tie the direction pin
the way I need it.

Cheers Mike

{Original Message removed}

2001\05\29@150535 by Andy N1YEW

picon face
it is a latch but not latch and HOLD

andy
----- Original Message -----
From: "Evans Michael E Maj ACC/XPPI" <spam_OUTMichael.Evans2TakeThisOuTspamLANGLEY.AF.MIL>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Tuesday, May 29, 2001 2:51 PM
Subject: Re: [PIC]: 8bit Data bus using a PIC16F84A.. A dream or reality?


> I'm venturing out on a limb here but I don't believe the 245 is a
latch...it
> is only a bi-directional buffer.  Like its brother the 244 which is only
one
> way, with its inputs on both side on the chip to ensure a messy layout.
> Note:  I would always use a 245 en lieu of a 244 and tie the direction pin
> the way I need it.
>
> Cheers Mike
>
> {Original Message removed}

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