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PICList Thread
'VoicePorts---Audio->A/D->UART->RS-232 TX & RX'
1996\08\23@040110 by John Welling

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I am reposting updated message as my mail server was down due to T-1
upgrade.
All response are most welcome amd encouraged!  Please RePost previous
responses!

PI>>> Telephone handset Audio into A/D converter sampling 8-bit bytes at
PI>>> 22,050 sample rate with serial data fed to UART(16550) outputting 57,600
PI>>> bit rate to MAX-232 RS-232 driver.

PI>Why bother with 22,050 samples/second with telephone handsets?  They
PI>were designed for a frequency range of ~300 to ~3000 Hertz.  Most of
PI>the carbon microphones and little speakers used in handsets just don't
PI>have the frequency response to justify this high a sample rate.

PI>Telephone companies chose 8,000 8-bit samples/second to give an upper
PI>frequency response of ~4000 Hertz (Nyquist limit).

'Scuse me for the bungled numbers.  I composed the Email from 3
categories of calculations not interchangeable.

The following is more reflective of reality:
57,600 baud Port * .8=46080 net data baud (less start & stop bits) /8
(bits per byte)=
5760 bytes/sec  / 2 = 2880 max Nyquist frequency.

I am going to try PIC 16c74 A/D sampling to its UART with BASIC and  'C'
code.
Does anyone know the Maximum A/D sampling and UART port speeds when
using:
1> PIC or ETI BASIC
2> compiled 'C' code (.OBJ)

ALSO, does anyone have info for intializing 16550 UART as standalone
FIFO-serial/parallel port interface

1996\08\23@091906 by Mark K Sullivan

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>I am going to try PIC 16c74 A/D sampling to its UART with BASIC and  'C'
>code.

You really ought  to do this in assembler.  It's not hard.  In fact, I bet it
will be much harder to make the project work in BASIC than it will be to learn
enough assembler.  It's going to be less than 100 lines of code, maybe less than
50.

- Mark Sullivan -

1996\08\23@094209 by root

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{Quote hidden}

       Having just finished a project with the 16550, I can tell you it
is very easy to use and initialize...  I would suggest checking out
National Semiconductor's web site (http://www.natsemi.com) where they have .PDF
documents on line with the complete 16550 manual being one of them
(you'll need to do a search on 16550 to find it).  The only thing I found
annoying about the 16550 was the Intel-ish practice of requiring the R*
and W* lines to only be active when CS* is.

Good Luck!


Larry Battraw

1996\08\23@150803 by peter

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Mark K Sullivan wrote:
> You really ought  to do this in assembler.  It's not hard.  In fact, I bet it
> will be much harder to make the project work in BASIC than it will be to learn
> enough assembler.  It's going to be less than 100 lines of code, maybe less
than
> 50.
>
> - Mark Sullivan -
Sorry this must be the most popular question
how do you start to program in assembler. I have mplab,embedded
controls handbook etc.
Will mplab run ok without hardware.
Is mplab good to start on
--
Peter Cousens
email: spam_OUTpeterTakeThisOuTspamcousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,

1996\08\24@061647 by John Welling
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PI>        Having just finished a project with the 16550, I can tell you it
PI>is very easy to use and initialize...  I would suggest checking out
PI>National Semiconductor's web site (http://www.natsemi.com) where they have .PDF
PI>documents on line with the complete 16550 manual being one of them
PI>(you'll need to do a search on 16550 to find it).  The only thing I found
PI>annoying about the 16550 was the Intel-ish practice of requiring the R*
PI>and W* lines to only be active when CS* is.

1> Is it possible to feed a sequence burst of init/config bytes to the 16550,
say from a PC parallel port buffered into the UART so that it could be a
standalone UART without CPU supervision?

2>Can the RX & TX sections be linked together as a standalone serial data time
shifter
( 8Kbps serial data in->Parallel FIFO Buffer->57.6 Kbps serial data out
)?

Many DANDY Answers received from around the World...Keep 'em coming!

TIA, John
.....sirejohnKILLspamspam@spam@bbs-la.com

1996\08\24@065913 by Clyde Smith-Stubbs

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John Welling <sirejohnspamKILLspamBBS-LA.COM> wrote:

(quoting someone else, presumably)

> PI>The only thing I found
> PI>annoying about the 16550 was the Intel-ish practice of requiring the R*
> PI>and W* lines to only be active when CS* is.

This is not correct - the RD, /RD, WR and /WR lines are ignored unless the
chip is selected. It is a little unusual in providing both active high and
low read and write lines - they are or'ed so you must tie the unused ones
to an inactive level.

>j 1> Is it possible to feed a sequence burst of init/config bytes to the 16550,
> say from a PC parallel port buffered into the UART so that it could be a
> standalone UART without CPU supervision?

You could do that, if you could arrange to drive the address lines as well. The
16550 has 8 register addresses, and intialising the chip requires writing
to a number of these. You may be able to use some of the control lines from
a parallel port as address lines.

> 2>Can the RX & TX sections be linked together as a standalone serial data time
> shifter
> ( 8Kbps serial data in->Parallel FIFO Buffer->57.6 Kbps serial data out

You would need an external baud rate generator for the receiver, a data latch
and some glue logic (a 16V8 GAL should do it). Something like the old AY-5-1013
would be easier - if there is an equivalent still available (they were a 40
pin chip with basically an independent RX and TX with non-multiplexed data
in and out and control).

Clyde

--
Clyde Smith-Stubbs       | HI-TECH Software,       | Voice: +61 7 3300 5011
.....clydeKILLspamspam.....hitech.com.au      | P.O. Box 103, Alderley, | Fax:   +61 7 3300 5246
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