This seven-inch card is for use in PC/XT/AT-class computers and contains two independent 24-bit groups. Two 50-wire ribbon interface cables plug into headers on the card and exit through a slot in the back-plate. Units required to meet EU "CE" requirements are supplied with blank mounting brackets. This permits using cabling methods that best fit your applications. Each 24-bit group uses a Programmable Peripheral Interface chip type 8255-5 (PPI). Each PPI, in turn, provides three 8-bit ports (Ports A, B, and C) which can be independently configured for either input or output. Port C can also be configured in four-bit groups for input or output. Type 74LS245 tri-state transceivers provide hysteresis correction for inputs and added drive capability for outputs. The direction of these buffers is automatically set as input or output according to software command. Also, the tri-state transceivers can be enabled or disabled under software control.
This card fully implements Mode 0 of the PPI. The card cannot be used in Mode 1 or Mode 2. A major feature of this card is that the state of all inputs can be monitored and, if any one or more bits change, a latched interrupt request can be generated. Thus, you can detect input state changes without need for software to continuously poll the inputs. After the interrupt has been serviced, the interrupt latch can be cleared by a software write. This change-of-state detection is particularly useful in robotics applications.
Interrupts are OR'ed together and may be directed to any "AT" interrupt level by jumper selection. IOD-48S occupies 16 bytes of I/O address space. The base address is set by DIP switch on the card and is selectable anywhere in the range of 000 to 3FF hex.