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IsThere a chip with multiple (4 or 8?) serial ports??

Discussion in 'Electronic Design' started by [email protected], Jul 5, 2007.

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  1. Guest

    I need to build devices for a Marine application that will receive
    multiple (4 or 8) serial signals. Typically the signals are 4800 baud,
    N,8,1 with a burst length of up to 80 characters, and a repetition
    rate of 1 to 2 per second. (These are NMEA signals). They are
    uncoordinated signals from individual devices such as GPS receivers,
    Engine monitoring instruments etc...

    I'm looking for a chip with multiple serial ports (actually receive -
    only would be OK here). I want to interface such a chip or chips to a
    PIC which will do a small amount of supervision, possibly filtering,
    and use it's main hardware UART or USB or a CAN controller to output
    data to a computer.

    I've searched thru MicroChip and some on Google etc. What I'd LIKE is
    a serial-port chip designed to interface to a microcontroller by SPI,
    serial, I2C etc. AND which has 4 to 8 serial ports.

    Anyone seen such a beastie?? Any other suggestions other than many
    single-channel USARTs (Ughh..)

  2. Rich Webb

    Rich Webb Guest

    The TI quads all seem to use a parallel bus interface. You could glue
    them to the micro via an SPI bus with a CPLD or small FPGA.

    Or, use a larger FPGA and instantiate as many UARTS as you need; check
    over at Possibly even incorporate the micro on it too.

    It might be simplest just go with the NXP (Philips) dual SPI chips,
    like the SC16IS752.
  3. What about using the GPIO pins of the PIC as software serial ports?

  4. Mook Johnson

    Mook Johnson Guest

    Would it be cheaper to just get a few small PICS that have a uart and SPI or
    i2c. Link them via a SPI or I2C bus to a master with more memory to buffer
    the data and sent it to the data computer.
  5. Greg Neill

    Greg Neill Guest

    What about adapting an existing multiport serial
    product? Here's one that adds up to 16 serial
    ports via USB:
  6. Maxim do a SPI uart chip but rather expensive.
    You can do it in software reasonably easily - 4800 baud is not especially taxing - you just need to
    sample an 8-bit input port at 3x the baud rate on a timer interrupt and then process each bit in
    In the past I've implemented 16 channels at 9600 baud on an ATMEGA88, so 8x4800 shouldn't be too
  7. It is actually quite simple to implement a serial port in software.
    Depending on processor speed, you can poll status for one or many
    status bits... use interrupts if you must.. PIC could do it.
    One fast PIC is all you need.

    If one wanted _many_ serial ports, fast hardware, and separate processing,
    filtering, and lots of IO to do something, then a small FPGA can be useful.
    You can easily fit >100 serial ports in a low cost FPGA, and perhaps
    if you actually needed a processor just use some core (free of buy IP).
  8. Guest

    Thanks for the suggestions, people!

    On Hardware:

    I'll look at the suggestions. Rich: What are the TI parts???
    The usb-to-4 and 8 ports I saw were all over $200.. way too much. And
    they are box-type products.
    I really want to be able to design a low-cost solution.

    On Software:
    I was originally inclined to bit-bang it too.. I agree the overhead
    with a timer-driven interrupt at 3x 4800 or maybe 3x 9600 wouldn't be
    bad with a fast PIC. And I believe that my code that would set up and
    sent out 80 character bursts on the hardware Serial port should be
    interruptible without much of a problem. And I know it worked for
    Mike :) at least on another processor...

    I don't have the time / money to become competent in synthesizing this
    kind of stuff into a FPGA. I understand it, worked once with others on
    instantiating a whole DSP design into multiple FPGAs, and know that my
    learning curve for the whole deal would be a lot more than debugging a
    PIC, when I already have the tools / debugger for that.

    Any pointers to PIC code, suggestions, etc. would be appreciated. This
    will be an open-source project for DIY Boating Electronics people. I
    hope to have XP code that will display gauges etc. along with
    Navigation software such as OziExplorer, and run this on a Mini-ITX
    board that can run fanless in a sealed box, like the VIA-EN12000EG at
    about 12 watts. The PICs are for interfacing NMEA devices and
    probably analog sensors into the low-power PC. The project will be
    attached to the Wiki at:

    I'm prototyping this stuff over the next month here in Vermont; In
    August I'm moving to Shenzhen in China for 2 or 3 years, and will
    continue the project from there, and get some older boat to run real
    stuff on.
  9. BobG

    BobG Guest

    Several atmel avr models have 4 serial ports mega644 and mega2560 I
    think... also avrfreaks has projects with source code for multiple sw
    uarts. New AVRs are clocking at 20Mhz... they're so fast they can do
    the sw uarts and go out for a smoke between characters.
  10. nospam

    nospam Guest

    One idea is not implementing 'serial' ports at all.

    The raw bit stream for an 80 byte message packet sampled at say 8 times the
    baud rate could be recorded in about 1k of RAM.

    If you play back that recording at 8 times the sample rate to an output
    'serial' port you effectively forward the message you received at 4800 to
    the output at 38k4.

    You need to detect the message packet boundaries which could probably be as
    crude as seeing a start bit at the beginning and x consecutive stop bits at
    the end.

    If you need to identify which channel the packet was received on then it
    would be possible to 'play back' a bit of hard coded bit stream prior to
    the recorded bit stream.

    A crude 8 to 1 and 4800 to 38k4 NMEA packet multiplexor. Hardware would be
    a fast uP with 8k of RAM and 9 I/O pins.

  11. Nico Coesel

    Nico Coesel Guest

    I've used multi-port UARTs from NXP before. I'm quite sure they have
    at least 4 port UARTs.

    But a small FPGA may be cheaper when it comes to components costs. A
    Xilinx Spartan 3AN with a microprocessor core and some UARTs for
    instance. In that case you'll have a single chip solution (the N in
    the part number stands for non-volatile so the FPGA can work
  12. Jim Backus

    Jim Backus Guest

  13. Rich Webb

    Rich Webb Guest

    Search Digikey for "UART" and then the 4 channel filter. Should get
    you to the TI TL16C-family e.g, TL16C554. Nice parts but the parallel
    access means that you'll tie up quite a few DIO lines on your micro.
    If it already has an address/data bus and supporting status lines and
    instructions then things are simplified a bit (no pun intended) since
    you can set up the UARTs as memory-mapped I/O.
  14. Philips (oops, sorry, NXP ;-) has some of these. Had a SC16C554 in my
    last design this is a quad uart chip, IIRC the C558 is the octal

    Don't know if 8 uarts can be done in software by digital IN's on a
    micro, but it might be worth thinking of it.

  15. Jasen Betts

    Jasen Betts Guest

    4800 is slow. bit-bang.
  16. TJ

    TJ Guest

    If all communications are async then you will have problems with
    multiple ports on a single pic. I have tried this with many barcode
    applications. The problem is that the uart must be waiting undisturbed
    to receive data. if you use interrupts, by the time you service
    interrupt the buffered data will be lost. I ended up using multiple
  17. Jasen Betts

    Jasen Betts Guest

    the trick is not to interrupt on the input data, but instead interrupt
    only on a timer and use the timer to drive the state-machines for each
  18. SC16IS752

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