Data Acquisition

The problems that may need to be considered when interfacing expansion cards to the IBMPC vary, depending on whether you are designing a board for a specific purpose or simplyplugging in an off-the-shelf board that requires configuring.While the basic considerations do not change, their complexity varies depending on thefunctions that the expansion board must perform.The primary considerations are:• Hardware compatibilityThese are the physical requirements such as connector configurations, boardsize, bus loading etc.• Addressing considerationsWhether the expansion board is addressed as part of the PC's memory or I/Omap, it is obviously important that each address is unique and does not conflictwith any other used addresses in the PC’s memory.• Timing requirementsThe timing of accesses to and from the memory and I/O as well as the systemboard timing for interrupts and DMA are strictly controlled within pre-definedlimits (this is what makes it a ‘standard’). Consideration of this timing is veryimportant since it greatly affects the efficiency of functions that the board mustperform, and can be affected by the physical hardware factors of the bus itself, thespeed of the CPU and the speed of the integrated circuits (ICs) used on theexpansion board.We will consider these issues here as they relate to an 8-bit 24 line programmable I/Ocontrol board interfacing to a standard ISA compatible bus. This is shown in Figure 4.18.