DIAMOND SYSTEMS ONYX-MM-DIO
48 DIGITAL I/O LINES WITH PROGRAMMABLE PORT DIRECTIONS
If you're looking for a basic 48-line digital I/O PC/104 module, then Onyx-MM-DIO is what you need. This module is the same as our Onyx-MM digital & counter/timer module but without the counter/timer and interrupt circuitry. This board still has the quality and attention to detail of our other modules, such as: 10K Ohm pull-up resistors on all I/O lines; all ports reset to 0 on power-up or system reset; connector pinouts compatible with our other digital I/O boards; and free software.
The 48 digital I/O lines on Onyx-MM-DIO are based on 2 82C55 ICs. They can be programmed for input or output in groups of 8 lines. Direct as well as strobed (latched) I/O modes are supported, and all I/O lines are connected to 10K Ohm pull-up resistors.
DIGITAL I/O OPERATION
Onyx-MM-DIO has 48 digital I/O lines using 2 82C55 ICs. Each chip has 24 I/O lines organized as three 8-bit ports, A, B, and C. All I/O lines are connected to 10KOhm pull-up resistors, and on power-up or system reset, all ports reset to input and are pulled high. A control register on the 82C55 chip allows you to program each port for input or output and for different operating modes, including basic I/O, strobed I/O, and bit set/reset.
Mode 0 operation provides basic input and output operations. No handshaking signals are used. This is the most common method of digital I/O and is useful for reading status signals, turning switches on and off, etc. All three ports can operate in Mode 0.
Mode 1 operation provides strobed I/O on ports A and B with handshaking signals provided on port C. In input mode, one signal is a strobe to latch data into the port, and a second signal is an acknowledge output. In output mode, one signal is used to indicate that the CPU has written new data to the port, and a second signal is an acknowledge input.
Mode 2 operation allows the use of Port A as a bidirectional data bus, with port C lines used for handshaking. Port A is normally in tristate mode. When the CPU writes new data to port A, an output signal indicates new data is available. In response, the external circuit strobes an acknowledge input signal, thereby enabling the output buffers on Port A. The external circuit can also latch new data into Port A with an input data strobe signal.
Bit set/reset mode enables individually setting (1) or resetting (0) any bit on Port C without having to read Port C and worry about masking or protecting unaltered bits. Note: The driver software shipped with Onyx-MM-DIO allows you to easily perform bit set and reset operations on any bit of any port.