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4-12 Theory of Operation
4.9 Programmed Logic Devices
Virtually all logic on the graphics board is contained in commercial parts
such the 34020, bus buffers, and programmed parts. The board uses
numerous Programmed Logic Devices (PLDs). This section will briefly
describe each part used and then outline the functions implemented by
them.
AMD MACH Field Programmable Gate Arrays (FPGA)
The lion's share of the programmed parts are MACH pin parts, where a
MACH210, MACH230, and MACH435 parts are used. The are
characterized by a high degree of flexibility. All parts are EEPROM
technology, which permits easy reprogrammability.
The MACH parts are essentially 26V16 building blocks linked by a
partially implemented crossbar switch built into a single package. The
MACH210 part has two blocks and the 230 has four blocks. Registered
and asynchronous I/O pins abound, and I/O and buried register per pin
capability, global clocks and resets are included. The MACH435 adds
input registers.
PAL22V10 Field Programmable Gate Array (FPGA)
The 22V10 part contains a general AND-OR array, with 8 OR terms that
can drive a particular output. Each output can be programmed for active
high or low, and can function as a tristate output as well. The parts are
EEPROM technology, which permits easy reprogrammability.