piclist 2000\05\30\181727a >
Thread: Microcontroller with 4 USARTs and 40 pins
www.piclist.com/techref/io/serials.htm?key=usart
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face BY : David VanHorn email (remove spam text)



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At 02:59 PM 5/30/00 -0700, Erik Reikes wrote:
>Something else to check out is the I2C UART chips from Maxim.  They have a
>family of chips that has either 232, 485, or logic level serial on one side
>and SPI or I2C on the other.  Very cool part.  I also believe they have a
>couple byte buffer to avoid overloading your micro.

Max 3100A with internal 232 buffers?
I'm using four of them, along with the on-chip uart, in an AVR project.
The SPI is a little tricky in that it's 16 bit words, and I can't afford to
hang around and bit-bang, but I worked out a way to do the whole mess
interrupt driven.

The hardest thing to do is to poll them and see which one interrupted you
(without having to receive data), but all you have to do is abort the
transaction, and you can have the uart hold the data while you figure the
rest out.

My four have the ints wire-or, so I have to go look at all four's status
before I know who to start pumping data from.

Why am I so busy? 7200 calculations/sec involving polar-rectangular
conversions, a little DSP, and then rect-polar again. (in addition to
parsing the stat-mux protocol that gives me four external full speed full
duplex 4800 baud ports, plus an internal virtual port, and a control
channel, with the on-chip uart talking to a PC at 115200)

I'm almost 50% busy!

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Subject (change) Microcontroller with 4 USARTs and 40 pins

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