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'Serial port(s) on PIC'
1996\10\30@004852 by tjaart

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Hi Everybody!

It seems that the absense of a second UART on the reasonably priced
PIC's (not the 17CXX) is one of the last benefits of the Intel chips
keep over Microchip's PICS.

Perhaps we can nag & nag & nag & nag Microchip until they include a
second UART on chips like the 16C74. Doing it in software is a pain in
the butt. Am I alone, or is there anybody else that agree?

Anyway, here's the code :

loop:
       movlw   nag_nag_nag_nag
       movwf   MICROCHIP
       goto    loop:

--
Friendly Regards

Tjaart van der Walt
______________________________________________________________
|  Another sun-deprived R&D Engineer slaving away in a dungeon |
|WASP International GSM vehicle tracking and datacomm solutions|
|           +27-(0)11-622-8686 | http://wasp.co.za             |
|______________________________________________________________|

1996\10\30@095138 by Byron A Jeff

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>
> Hi Everybody!
>
> It seems that the absense of a second UART on the reasonably priced
> PIC's (not the 17CXX) is one of the last benefits of the Intel chips
> keep over Microchip's PICS.

Um exactly which Intel parts have the second UART and what's their cost?
The 8051, 803[12], and 8751 don't right?

>
> Perhaps we can nag & nag & nag & nag Microchip until they include a
> second UART on chips like the 16C74. Doing it in software is a pain in
> the butt. Am I alone, or is there anybody else that agree?

Well it may be useful but I've found that PICs make very good software UART
engines with some caveats. Specifically:

1) Works well in half duplex operation
2) Doesn't require a lot of time intensive work while serial stuff is going on.

I've just finished a half duplex software UART that will do 38400 using a
14.7456 Mhz crystal. With a 19.6608 Mhz crystal you can get 38400 operation
(38400 * 512 -> 19.6608 Mhz) and have time leftover to do other stuff.

My UART implementation uses precise delays and no interrupt. However it would
be fairly simple to convert it to using interrupts for delays and a state
machine. Then the PIC could do other work and get interrupted for each bit
to be transferred.

The other thing I like about software UARTS is that I can pick and choose the
pins that I want to run them on. And potentially I could build several of
them into a single PIC.

Also there are some fairly simple hardware UARTS that could easily be attached
to a PIC. One of my favorites is the Signetics 2691. Comes in a 28 pin skinny
DIP, has a 4 byte receive buffer, and has an extra timer on board, along with
the standard baud rate generator.

I'm designing a portable MIDI sequencer. Each MIDI channel requires a UART.
I'm planning on using the Cirrus Logic CL-CD-180 8 port UART. Each channel
has 8 bytes of send and receive buffers and the part comes in a 84 pin PLCC
so it doesn't take a whole bunch of space. 2 PIC ports and a latch are required
for interfacing.

And of course if you're tight for space just program another small PIC as
software UART and interface it to the main PIC. Cheaper than a real UART,
takes less space and power, and you already have them in your box.

I haven't really used a UART since I've started programming PICs not that I
think about it. All of the serial interfaces I've built in the last two years
are software PIC UARTs.

BTW I've finally figured out the secrets to precise delays:

1) Never reset your timer, let it free run.
2) Use another register to store the end of the delay. Update that register
instead of the timer.
3) Use a crystal that is a integral multiple of the bit rates you want to
produce. Use 18.432 Mhz if you need 57.6K and 115.2K or the 19.6608 Mhz if
you need only up to 38.4K.

My last crack at UART code produced a UART that only worked up to 2400 BPS
because I reset the timer. Using the 14.7456 Mhz crystal, a free running
timer, and an extra register to hold the end of the next delay, 38.4K was
no problem. My next test is 57.6K and 115.2K because I'll scale back the
prescale from 1:16 to 1:8.

Anyway PIC software UARTS are a godsend for me. I know I can pull together
a PIC and a MAX232 and have a serially programmable I/O controller in a
matter of minutes.

BAJ

1996\10\31@030925 by Werner Terreblanche

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Tjaart van der Walt <spam_OUTtjaartTakeThisOuTspamWASP.CO.ZA> wrote:

>Perhaps we can nag & nag & nag & nag Microchip until they include a
>second UART on chips like the 16C74. Doing it in software is a pain in
>the butt. Am I alone, or is there anybody else that agree?

Tjaart

 Maybe its time you should consider using the CCS C compiler.  I
recently started using it and one of the most usefull functions is
its capability to add a software serial port on ANY of the pic
devices.  What a pleasure to be able to use printf statements on
devices like the PIC16C84!  And if you need two serial ports on one
device its no problem at all, because the compiler already caters for
that.  And its defineteyl not a pain in the butt to implement.

I do all my development work now using that compiler and I add printf
statements while debugging my software.  Once I'm happy that its
working I just delete the printf statements and re-compile.  Its
really worth the $99 that you pay for it.

Regards
Werner
--
Werner Terreblanche   Tel +27 21 7102251   Fax +27 21 721278
.....wterrebKILLspamspam@spam@plessey.co.za (work) OR wernerspamKILLspamaztec.co.za  (home)


'Serial port(s) on PIC'
1996\11\05@132229 by Mike Geipel
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Tjaart van der Walt <.....tjaartKILLspamspam.....WASP.CO.ZA> wrote:

> Perhaps we can nag & nag & nag & nag Microchip until they include a
> second UART on chips like the 16C74. Doing it in software is a pain in
> the butt. Am I alone, or is there anybody else that agree?

Yes!  I *really* need a processor with an SPI channel and two UARTs.
(I don't have the option of using a software UART...)

I've heard that the 17C752 will have two UARTs, but not an SPI port.  :-(
(Actually, it's too expensive for my application anyway.)
I'd really love to see the 16C65A with a second UART.  Hint, hint.


Although I hate using an external UART with the 16C65A, I don't have
much choice...  so here's my question:
 Does anybody know about a really *small* UART?
 Perhaps something in an SOIC-14 package?  (Smaller is better!)


advTHANKSance (THANKS in advance),
--
Mike Geipel                  (N4IXJ) | Eurotherm Controls Inc.
Telephone:       (703) 471-4870 x387 | 11485 Sunset Hills Road
"EraseMEMike.Geipelspam_OUTspamTakeThisOuTControls.Eurotherm.COM" | Reston, VA   22090-5286

1996\11\08@042839 by liebchen

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Mike Geipel wrote:
> > Perhaps we can nag & nag & nag & nag Microchip until they include a
> > second UART on chips like the 16C74. Doing it in software is a pain in
> > the butt. Am I alone, or is there anybody else that agree?
>
> Yes!  I *really* need a processor with an SPI channel and two UARTs.
> (I don't have the option of using a software UART...)
>
> I've heard that the 17C752 will have two UARTs, but not an SPI port.  :-(
> (Actually, it's too expensive for my application anyway.)
> I'd really love to see the 16C65A with a second UART.  Hint, hint.

Well, you may have heard the wrong. Look at the datasheet of the 17C752,
it has
two UARTS/SCI and one SSP (either I2C or SPI). So it has what you want!

regards Wolfram

--

+------------------------------------------------+
! Wolfram Liebchen, Forschungsinstitut fŸr Optik !
! liebchenspamspam_OUTffo.fgan.de                    !
+------------------------------------------------+

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