"The Laboratory Interface provides 16 optically isolated
connections each of which may function as input or output to the computer
system. The opto-isolators and an INS 8154 integrated circuit are amongst the
components carried on a standard Eurocard (100 x 160mm) which plugs on to the
Acorn computer bus. A remote circuit board with 16 power drivers and LED
indicators may be connected by up to 25 metres of 40 way flat ribbon cable to
the Eurocard.
The remote circuit board has 16 connections each of which
is set to input or output using a switch. In its output mode each connection can
drive loads drawing current at up to 3 amperes each from the remote supply
voltage which may be in the range 6 to 48v. A catching diode on each output
allows inductive loads to be used. In input mode each connection is driven by
contact closures to the remote supply common. An LED indicates the state of each
connection in input or output mode.
The remote supply voltage is optically isolated from the
Acorn system on the interface Eurocard giving the computer immunity to
electrical noise generated by the load switching. Noise produced by other
equipment at the remote station is also isolated and ground loop problems
encountered in the laboratory environment are eliminated. The remote supply can
be different to the computer 0 volt line by as much as 48V peak.
Acorn's ONLIBASIC may be used to configure the 16
input/output ports of the INS 8254 such that they match the modes set by the 16
switches at the remote station. Inputs are then read and outputs are then driven
by the program. The program may be synchronised to real time using interrupts
which are generated by circuitry on the interface Eurocard with a periodic time
of 10 milliseconds.
Schematics:
