GAL 22V10D PLCC-28

programmable-logic device

The GAL22V10 has a variable number of product terms per OLMC.
Of the ten available OLMCs, two OLMCs have access to eight
product terms (pins 14 and 23, DIP pinout), two have ten product
terms (pins 15 and 22), two have twelve product terms (pins 16 and
21), two have fourteen product terms (pins 17 and 20), and two
OLMCs have sixteen product terms (pins 18 and 19). In addition
to the product terms available for logic, each OLMC has an additional product-term dedicated to output enable control.
The output polarity of each OLMC can be individually programmed
to be true or inverting, in either combinatorial or registered mode.
This allows each output to be individually configured as either active
high or active low.
The GAL22V10 has a product term for Asynchronous Reset (AR)
and a product term for Synchronous Preset (SP). These two product terms are common to all registered OLMCs. The Asynchronous
Reset sets all registers to zero any time this dedicated product term
is asserted. The Synchronous Preset sets all registers to a logic
one on the rising edge of the next clock pulse after this product term
is asserted.
NOTE: The AR and SP product terms will force the Q output of the
flip-flop into the same state regardless of the polarity of the output.
Therefore, a reset operation, which sets the register output to a zero,
may result in either a high or low at the output pin, depending on
the pin polarity chosen

Each of the Macrocells of the GAL22V10 has two primary functional
modes: registered, and combinatorial I/O. The modes and the
output polarity are set by two bits (SO and S1), which are normally
controlled by the logic compiler. Each of these two primary modes,
and the bit settings required to enable them, are described below
and on the following page.
REGISTERED
In registered mode the output pin associated with an individual
OLMC is driven by the Q output of that OLMC’s D-type flip-flop.
Logic polarity of the output signal at the pin may be selected by
specifying that the output buffer drive either true (active high) or
inverted (active low). Output tri-state control is available as an individual product-term for each OLMC, and can therefore be defined
by a logic equation. The D flip-flop’s /Q output is fed back into the
AND array, with both the true and complement of the feedback
available as inputs to the AND array.
NOTE: In registered mode, the feedback is from the /Q output of
the register, and not from the pin; therefore, a pin defined as registered is an output only, and cannot be used for dynamic
I/O, as can the combinatorial pins.
COMBINATORIAL I/O
In combinatorial mode the pin associated with an individual OLMC
is driven by the output of the sum term gate. Logic polarity of the
output signal at the pin may be selected by specifying that the output
buffer drive either true (active high) or inverted (active low). Output tri-state control is available as an individual product-term for
each output, and may be individually set by the compiler as either
“on” (dedicated output), “off” (dedicated input), or “product-term
driven” (dynamic I/O). Feedback into the AND array is from the pin
side of the output enable buffer. Both polarities (true and inverted)
of the pin are fed back into the AND array