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'addressing external eprom'
1999\06\15@041550 by yasser osman

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<x-flowed>hello,anybody has suggestions for addressing external eprom by
PIC16c84.
thanks.


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1999\06\15@045327 by Markus Rohe

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face
On Tue, 15 Jun 1999, yasser osman wrote:

> hello,anybody has suggestions for addressing external eprom by
> PIC16c84.
> thanks.
>
>
> ______________________________________________________
> Get Your Private, Free Email at http://www.hotmail.com
>

It depends on how many eprom cells you need and how many i/o lines you
have left in your application.

1) for 256 or 512 (2^8 or 2^9) eprom words, you coud use prot B and the
rest of your eprom adress pins can be controlled with dip switches (bank
switching)

2) take 2 74LS299 ("non-clipping" shift register) to get 16 outputs out of
3 PIC i/o lines to control a
64K (?) Eprom completely from your 16C84

I hope I could help you, for datasheets of the 74299 have a look at
<http://www.ti.com>

Friendly Regards
Markus Rohe

1999\06\15@065700 by Byron A Jeff

face picon face
>
> hello,anybody has suggestions for addressing external eprom by
> PIC16c84.

Sequentally or random? If it's sequentally it's pretty easy. Use a 74HCT393
dual 4 bit ripple counter. You'd need two of them to address up to 64K, 3
to address up to 16M. Wire a 2 wire interface to the PIC, clock and clear,
then wire the outputs of the counters to the address lines of the EPROM.
You can then use all of port B as the data interface.

If it's random you'll probably need either a serial interface or possibly
you could wire a set of 74HCT573 latches for the address and use a 74HCT541
buffer as the interface to the data lines.

Depending on how many extra pins you need you could build 4 wire interfaces
using half of the latches and buffers.

If EPROMs are not an absolute requirement, then you could take a look at
Atmel's DataFlash EEPROMs, then come in sizes up to 2 Mbytes and have a
serial interface that'll only take 3 pins of the 16C84.

Another possibility is moving up to a PIC16F877 which gives you the same
programming interface as the c84, but with 33 I/O pins to interface with.
Wiring wise it'll be less in the long run than the 74 series parts.

Hope one these ideas help.

BAJ

1999\06\15@122016 by w. v. ooijen / f. hanneman

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> hello,anybody has suggestions for addressing external eprom by
> PIC16c84.

use i2c (2 pins only), or is that not the type of answer you want?
Wouter

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