Manual Number: 00650-014-4
Page 3-2
AD12-8 Manual
The Counter #2 clock is supplied from the output of Counter #1 as noted previously. The gate is
pulled up to +5V and is not accessible at the I/O connector. The Counter #2 output can be used to
start preprogrammed A/D conversions if the TMR/EXT jumper is installed in the TMR position.
A/D Conversion Start
An A/D conversion can be started from Counter #2 if the TMR/EXT jumper is in the TMR posi-
tion. Alternatively, A/D conversions can be initiated by negative pulses on Digital Input 0 if the
TMR/EXT jumper is in the EXT position.
A/D conversion start can also be initiated in software by a computer write to BASE A
1 or, if the AUTO jumper is installed, by a computer read of BASE A 0. The AUTO
mode is especially useful when high throughput is required.
Interrupts
Interrupts originating from either completion of A/D conversions or from an external source (pin
24) are supported. Interrupts are enabled by setting the IEN bit of Control Register #1 high. Selec-
tion of the interrupt source is made by jumper. Install a jumper in the EOC position at jumper
location EXT/EOC to select interrupts caused by the end-of-conversion signal. Install a jumper in
the EXT position at jumper location EXT/EOC to select external interrupts.
The end-of-conversion interrupt is supported by the AD12-8 software drivers. If you desire to use
external interrupts, then you must supply your own interrupt service routine. NOTE: The end-of-
conversion interrupt is intended to be used only when A/D conversions are started by the counter/
timer(install jumper in the TMR position of the TMR/EXT jumper), or by an external event (install
jumper in the EXT position of the TMR/EXT jumper). If the AUTO jumper is installed, or
Software Start is used, the use of interrupts will degrade card speed.
Interrupt levels IRQ2 through IRQ7 are available. The desired level is selected by installing a
jumper in one of the jumper locations marked IRQ2 through IRQ7.
Digital I/O
The AD12-8 card provides eight individually programmable digital inputs/outputs in addition to
eight digital outputs OP0-OP3, GN0-GN2, and USER. These latter eight outputs operate strictly
under software control.
Eight jumpers determine the input/output configuration of the eight digital lines identified as DIO0-
DIO7. If no jumpers are installed, all eight lines are configured as inputs. Installation of a jumper
at locations DO-D7 convert the corresponding line to an output.
Digital inputs are read from a register at BASE A 3. Digital outputs are written to a
register at BASE A 0. Note that full feedback is provided for the digital outputs be-
cause output status can be read back through the register at BASE A 3.
