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ISL - Local Bus

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Summary

The Inventio Software standard : the simplest, cheapest way to interconnect PCB's inside a unit's enclosure, when only low data rates are required.
Maximum distance 1.0m.

Features

  • Up to six "ports" on up to 6 separate boards with no demultiplexing on each board. Up to 32 "ports" with simple address decoding.
  • Direct connection to ADCs, DACs and digital i/o.
  • +12V nominal power lines supplied with control signals.
  • One interrupt line for quick response to inputs.
  • Roughly 200k Baud maximum transfer rate ( processor and software dependent - see Notes below ).
  • A 26 way IDC connector and ribbon cable connects all PCB's within a unit.
  • ISR signals on pins 3 and 4, allow remote communication from any local board.

    Hardware

    26 way IDC ribbon cable with the following pin connections: ( input/output is wrt Host end )

    1 0V 0V supply ground return for +12V
    2 +12V +12V supply main power supply line
    3 RS485- P3.0/1/Q0 serial ISR remote bus
    4 RS485+ P3.0/1/Q0 serial ISR remote bus
    5 Int P1.5/INT3- input interrupt, Host has 4k7 pull-down
    6 Drx P1.4/INT2 input data in
    7 Clk P1.1 output clock
    8 Dtx P3.5/T1 output data out
    9 Sel0 ISL0 output select n
    10 Sel1 ISL1 output "
    11 Sel2 ISL2 output "
    12 Sel3 ISL3 output "
    13 Sel4 ISL4 output "
    14 Sel5 ISL5 output "

    15 Relay0 ISL6 output relay output 0
    16 +5V supply local supply
    17 Relay1 ISL7 output relay output 1
    18 Counter0 P3.4/T0 input pulse counter 0
    19 Counter1 P1.0/T2 input pulse counter 1
    20 Pstrobe Q1 output printer strobe

    21 0V 0V supply ground
    22 Serial2 TX5V P1.2 output un-buffered serial
    23 Serial2 RX5V P1.3 input un-buffered serial
    24 Serial2 DIR5V Q2 output un-buffered direction1
    25 Serial2 DIR5V Q3 output un-buffered direction2
    26 +5V supply local supply

    Typical Interfaces

    Since all the signals are under software control at the Host end, an inverted signal ( e.g. inverted Seln ) does not require any extra hardware. SelN means one of Sel0 .... Sel5.
    1) ADC - LTC1288 Pin 1 = SelN, pin 4 = 0V, pins 5 and 6 = Drx, pin 7 = Clk, pin 8 = +5V
    2) DAC - AD7543 Pin = 4 = Clk, pin 5 = inverted SelN, pin 7 = Dtx, pin 12 = 0V, pin 14 = +5V
    3) Digital Input - 74HC589 Pin 8 = 0V, pin 9 = Drx, pin 10 and 12 = inverted SelN, pin 11 = Clk, pin 14 = Drx, pin 16 = +5V
    4) Digital Output - 74HC595 pin 8 = 0V, pin 11 = Clk, pin 12 = SelN, pin 14 = Dtx, pin 16 = +5V
    5) Parallel printer port - a) 74HC595 pin 8 = 0V, Pin 11 = Clk, pin 12 = SelN, Pin 14 = Dtx, Pin 16 = +5V b) Pstrobe to strobe line c) NAND of error lines to Dout = pin 6 via tri-state buffer ( or to 74HC589 as in 3 above ) d) Printer ack to Int = pin 5 via tri-state buffer or diode

    Notes:
    The maximum total continuous current is 1 Amp (IDC pin rating).

    The data transfer rate depends on the time taken for the processor to toggle the required bits. Data may be sent and recieved at the same time : for an DS80C320 running with a 14.7456MHz clock, 16 bits of data can be transferred in both directions in roughly 0.4 mS, which is equivalent to a full duplex 200k Baud rate. This is, of course, using the processor all of the time, unlike when a hardware serial port is used.

    Devices which have both a serial in and serial out pin may be connected in series, but bear in mind the time taken to transfer data. For example, 16 74HC595's will give 128 bits of digital output, all on one "port", will take roughly 1mS to load.

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