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Thurlby Logic Analyser LA4800 RS423

Discussion in 'Electronic Equipment' started by Aly, Jul 21, 2006.

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  1. Aly

    Aly Guest


    Has anyone had any experience of hooking up an LA4800/3200 to a PC running
    it's LATALK Dos software?

    The RS423 interface is described as RS232 compatiable but if you plug in a
    straight RS232 cable from PC to LA then the PC doesn't see the LA.

    I've looked into this further and RS423 is almost a completely different
    standard and levels to RS232. So a bit confused as to how the interface is
    described as RS232 compatiable.

    Thurlby have been brilliant in that they supplied the LATALK software a few
    weeks back but with the LA4800 being discontinued and unsupported the
    information I need isn't readily at hand.

    Any ideas?

    Thanks kindly,

  2. 423 and 232 are to all intents the same for the majority of applications - 232 just swings further.
    bear in mind that this instrument dates back to when computers other than PCs were not uncommon ,
    and so the D9 pinout may not be expecting to be plugged directly into a PC without some
    pin-juggling. You may also need to do things like loop back handshake pins.

    Start by confirming the TX/RX direction - at the connector, 0V will be in input (receive) and more
    than a volt negative will be an output (transmit)
  3. Aly

    Aly Guest

    Hi Mike,

    This is what I have so far from the manual..
    The analyser is fitted with a bi-directional RS-423 serial interface which
    is fully compatiable with equipment fitted with an RS-232 interface. The
    interface can be operated at either 1200 or 9600 baud (selectable from the
    configuration screen).

    The connections for the interface are as follows:

    5 4 3 2 1
    9 8 7 6

    1 = +5V
    2 = DATA IN
    3 = DATA OUT
    4 =
    5 = GND
    6 =
    7 = RTS (O/P)
    8 = CTS (I/P)
    9 = -5V

    Note that the interface in not isolated and that signal ground for the
    interface is directly connected to chassis ground.

    The interface is used for the printer output, and can be used for
    bi-directional transfer of data and for full remote control of the analyser.
    The commands for data transfer are listed in Appendix B.

    So that's about it. I've tried patching what seems like all sorts of
    combinations TX to RX, TX to TX,. CTS to CTS, CTS to RTS. I've even tried
    doing thing on an older generation genuine IBM PC-AT which usually when
    comms issues arise solves most problems.

    From what I've read so far on the net RS232 and RS423 are two almost
    completely different standards, so am wondering if anyone has done this,
    been in this position etc?

    Kind thanks,

  4. As PCs put data out on pin 23, you will need to crossover pins 2/3. I'd suggest looping back the
    handshake lines at each end, i.e. link pins 7/8 at each end, and maybe also DTR to DSR at the PC
    No they are not. The only difference is the voltage swing, and this can be ignored in pretty much
    all cases as RS423 levels will work a 232 receiver and a 423 receiver will tolerate RS232 12V
    swings. .
  5. Aly

    Aly Guest


    2 - 3
    3 - 2
    4 *
    5 - 5
    6 *
    7 - 8
    8 - 7

    (-) = link to
    (*) = short with

    Many many thanks Mike!! Cheered me up that has :)

    Huge thanks,

    Alison, Cambridge UK
  6. Aly

    Aly Guest

    With Mike's help.. to reiterate. The correct wiring between a standard PC
    9-pin serial port and a Thurlby LA3200/4800 is:

    2 - 3
    3 - 2
    4 *
    5 - 5
    6 *
    7 - 8
    8 - 7

    (-) = link to
    (*) = short with on PC side
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