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'[PIC] Favorite dual UART?'
2005\01\19@174120 by Harold Hallikainen

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Does anyone have a favorite dual UART to hang on a PIC with a parallel interface?
In the past I've used the 2681. I'm looking at the 16c552. I need a parallel
interface since I just found I run out of time using the SPI interface on the
MAX3140.

Thanks!

Harold


2005\01\20@020817 by Wouter van Ooijen

face picon face
> Does anyone have a favorite dual UART to hang on a PIC with a
> parallel interface?

Pic any two PICs with a UART, or one PIC with two.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2005\01\20@140157 by Mike Harrison

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face
On Thu, 20 Jan 2005 08:06:13 +0100, you wrote:

>> Does anyone have a favorite dual UART to hang on a PIC with a
>> parallel interface?
>
>Pic any two PICs with a UART, or one PIC with two.

..or one with one UART and do the other in software.


2005\01\20@144654 by Peter Johansson

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face
Mike Harrison writes:

> On Thu, 20 Jan 2005 08:06:13 +0100, you wrote:
>
> >> Does anyone have a favorite dual UART to hang on a PIC with a
> >> parallel interface?
> >
> >Pic any two PICs with a UART, or one PIC with two.
>
> ..or one with one UART and do the other in software.

Or just go with the SX and do up to 8 UARTs in software.  Certain
restrictions apply, of course, but doing dual UARTs in software on a
SX-18 that can be had for under two bucks is certainly worthy of
consideration...

-p.

2005\01\21@121501 by Harold Hallikainen

face picon face
Two of the uarts need to run at 250kbps and one at 500kbps. Can an SX
really do that in software?

Thanks!

Harold

> Or just go with the SX and do up to 8 UARTs in software.  Certain
> restrictions apply, of course, but doing dual UARTs in software on a
> SX-18 that can be had for under two bucks is certainly worthy of
> consideration...
>


--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\01\21@122055 by Harold Hallikainen

face picon face
But I need three uarts! It seems lower cost to do a PIC with one and
another duart chip with two.

Thanks for the ideas!

Harold


>> Does anyone have a favorite dual UART to hang on a PIC with a
>> parallel interface?
>
> Pic any two PICs with a UART, or one PIC with two.
>
> Wouter van Ooijen


--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\01\21@124801 by Bob Axtell

face picon face
Yep.

Harold Hallikainen wrote:

{Quote hidden}

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2005\01\21@125528 by Mark Jordan

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face

       Maybe the Atmel ATMEGA128 with dual USART and a TWI channel.
       Or the good old Z85C30 SCC...

       Mark Jordan

On 21 Jan 2005 at 9:20, Harold Hallikainen wrote:

{Quote hidden}

> --

2005\01\21@131750 by William Chops Westfield

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On Jan 21, 2005, at 9:14 AM, Harold Hallikainen wrote:

> Two of the uarts need to run at 250kbps and one at 500kbps.

Very few uarts are spec'ed to run at that speed, especially if you want
to retain the reliability introduced by a 16x clock.  the 2681 you
mentioned
tops out at 125kbps.

Also, even with a uart doing serial/parallel conversion, I think most
micro
controllers will have trouble keeping up with that sort of datarate
(200k
bytes/second!)

The deep-fifo windows-compatible 16550 extensions may be your only
choice.

BillW

2005\01\21@135656 by Mike Harrison

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face
On Fri, 21 Jan 2005 10:17:51 -0800, you wrote:

>On Jan 21, 2005, at 9:14 AM, Harold Hallikainen wrote:
>
>> Two of the uarts need to run at 250kbps and one at 500kbps.
>
>Very few uarts are spec'ed to run at that speed, especially if you want
>to retain the reliability introduced by a 16x clock.  the 2681 you
>mentioned
>tops out at 125kbps.
>
>Also, even with a uart doing serial/parallel conversion, I think most
>micro
>controllers will have trouble keeping up with that sort of datarate
>(200k
>bytes/second!)
>
>The deep-fifo windows-compatible 16550 extensions may be your only
>choice.
>
>BillW

Take a look at the Xilinx XC9536XL CPLD - should be able to do a couple of uarts as fast as you
like, and very low cost - below $2,  XC9572 could do a few bytes of fifo if you want it.



2005\01\21@135726 by Bob Axtell

face picon face
But it would be trivial for a 100MIPS Ubicom chip. The algorithm would
be to time the
ON and OFF times of all bits, and when the sum of both bits indicated
that the stop
bit was in process, quickly determine the byte's value and store it or
shove it out (to
a PIC with an 8-bit BUS plus a 2-bit address, a total of 10 pins needed
+ a dataready pin).

At 100MIPS, 4 complete 250Kb UARTS should be possible, or 8 125kb or slower
UARTS.  The SX could be run cooler at 50Mhz if the speeds are
reasonable, such as
19.2Kb. If 8 uarts, the transfer bus would have 11 bits,  a dataready
bit, and each
UART would have RX and TX.

A 4-uart system needs 19 I/O pins, while if 8 uarts are needed, a total
of (11+16) = 28 pins
are used. I am not certain that Ubicom makes such a large device.

Its still the cheapest solution, though. I've done dual 1200b uarts with
a PIC16C57 at 20Mhz.

--Bod

William Chops Westfield wrote:

{Quote hidden}

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2005\01\21@140036 by Wouter van Ooijen

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> But I need three uarts! It seems lower cost to do a PIC with one and
> another duart chip with two.

Which UART chip do you have in mind that costs less than a small PIC or
SX?

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2005\01\21@143412 by Peter Johansson

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face
Bob Axtell writes:

> At 100MIPS, 4 complete 250Kb UARTS should be possible, or 8 125kb or slower
> UARTS.  The SX could be run cooler at 50Mhz if the speeds are
> reasonable, such as
> 19.2Kb. If 8 uarts, the transfer bus would have 11 bits,  a dataready
> bit, and each
> UART would have RX and TX.

My experience is that most SX chips top out just below 100 Mhz, at
least with a 5.0v supply.  You might be able to eek out a bit more by
raising supply voltage, but it's not something I'd recomend.  When you
run them above 50 Mhz they sure do get hot but fortunately, the heat
doesn't seem to effect reliability.  Still and all, if you want to
push the limits of the chip a heat sink wouldn't be a bad idea.

-p.

2005\01\21@180305 by James Newtons Massmind

face picon face
With the SX running at 50 to 75 MIPS, I believe it would be possible to get
basic uart functions at those speeds.

The ISR calculator at
www.sxlist.com/techref/scenix/isrcalc.asp?clock=75&baud=500000&fErr=0
.25
Shows that with an ISR running 500kHz you still have 150 instructions
available between interrupts. You should be able to shift out a bit, count
every other interrupt and shift two other bits every other int as well as
check status, start, stops and so on, all within 150 instructions.

Are you receiving at 250 and xmitting at 500? Or the other way round?

You can transmit from multiple pins with no extra cycles by using parallel
operations. E.g. 8 tx ports take only a few more cycles than 1. Receiving is
a little more difficult, but parallel operations can still apply to some
degree.

Just to get an idea of what can be done, this little snippet is the heart of
a program that xmits at 500Kbps with a 4Mhz clock (less than a 10th the
standard speed of an SX and almost a 20th the max rated speed)
http://www.sxlist.com/lib/io/osi2/serial/rs232at500kbps_sx


; serial tx
; assumes PORTB1 initially on high state

       mov        W, >>data
       xor        data, W

       mov        W, #1
       xor        RB, W        ;start bit

       snb        C
       xor        RB, W        ;b0

       snb        data.0
       xor        RB, W        ;b1

       snb        data.1
       xor        RB, W        ;b2

       snb        data.2
       xor        RB, W        ;b3

       .
       .
       .

       nop
       setb        RB.0        ;


And it won't kill you to add the SX to your bag of tricks, see my other
post... They just dropped the price of the dev kit to $99 for the deluxe or
$79 for the debugger (like ISD) only.

---
James Newton, Host of SXList.com
jamesspamKILLspamsxlist.com 1-619-652-0593 fax:1-208-279-8767
SX FAQ / Code / Tutorials / Documentation:
http://www.sxlist.com Pick faster!





> {Original Message removed}

2005\01\21@185324 by James Newtons Massmind

face picon face
Actually Ubicom lowered the spec to 75Mhz. You can typically push them to
100, but 75 is more than enough for this (and most) applications.

---
James.



> {Original Message removed}

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