Model IOD-64 accepts up to 64 bits of Digital I/O and the card is organized into eight 8-bit ports. Input voltages can range up to 30 VDC. This card is particularly useful for interface between an ISA-Bus computer and industry-standard, optically-isolated, solid-state I/O module mounting racks. Up to four 16-position I/O racks can be controlled and
each point is directly addressable by the host computer.Variable I/O-mapped addressing allows you to select eight consecutive addresses plus a separate control port from any I/O addresses between 200 hex and 3FF hex. In addition, you can drive four of the host's interrupts from inputs applied to IOD-64. Read/Write Select Logic manages all data transmission between the computer and the I/O ports. There are five inputs to the select logic:
- Reset: When this line goes high, either on power-up or during a low-line voltage loss, it clears the Output Control Latch disabling all output ports. This assures that there will be no spurious outputs.
- Address Enable (AEN): When this line is driven low, it enables the PC I/O channel. The Read/Write Select Logic then checks the value on the address bus by comparing that address to the I/O Port and Control Addresses.
- I/O Write Command (IOW): When this line is low and the address comparison is true, the IOD-64 card reads data from the data bus.
- I/O Read Command (IOR): When this line is low and the address comparison is true, the IOD-64 card writes data to the data bus.
- Address (ADDR): These ten lines are used to address the Control Port and I/O Ports.
When the Data Bus Buffer is enabled by the Read/Write Select Logic, it permits data transfer between the host computer and the IOD-64. The Output Control Latch disables any or all of the eight 8-bit I/O ports. Inputs to the Output Control Latch are:
- Data from the host computer data bus.
- When the PC-Reset line is high, it automatically clears the Output Control Latch which, in turn, disables all outputs as previously described.
- When the Output Control Latch is enabled by the Read/Write Select Logic, it will disable individual ports as required by programming.
The IRQ Control, when enabled by the Read/Write Select Logic, routes external inputs received from any or all of the last four inputs of PORT 7 to IRQ4 through IRQ7 of the host computer.
PIN CONNECTIONS
Four 50-pin headers are provided; one for each group of 16 bits. Sixteen bi-directional data lines are alternated with 16 ground lines on each connector. Also, 5 VDC power is available and digital ground.
