MAX 7000A Programmable Logic Device Data Sheet
Open-Drain Output Option
MAX 7000A devices provide an optional open-drain (equivalent to
open-collector) output for each I/O pin. This open-drain output enables
the device to provide system-level control signals (e.g., interrupt and
write enable signals) that can be asserted by any of several devices. This
output can also provide an additional wired-ORplane.
Open-drain output pins on MAX 7000A devices (with a pull-up resistor to
the 5.0-V supply) can drive 5.0-V CMOS input pins that require a high
VIH. When the open-drain pin is active, it will drive low. When the pin is
inactive, the resistor will pull up the trace to 5.0 V to meet CMOS VOH
requirements. The open-drain pin will only drive low or tri-state; it will
never drive high. The rise time is dependent on the value of the pull-up
resistor and load impedance. The IOL current specification should be
considered when selecting a pull-up resistor.
Programmable Ground Pins
Each unused I/O pin on MAX 7000A devices may be used as an
additional ground pin. In EPM7128A and EPM7256A devices, utilizing
unused I/O pins as additional ground pins requires using the associated
macrocell. In MAX 7000AE devices, this programmable ground feature
does not require the use of the associated macrocell; therefore, the buried
macrocell is still available for user logic.
Slew-Rate Control
The output buffer for each MAX 7000A I/O pin has an adjustable output
slew rate that can be configured for low-noise or high-speed performance.
A faster slew rate provides high-speed transitions for high-performance
systems. However, these fast transitions may introduce noise transients
into the system. A slow slew rate reduces system noise, but adds a
nominal delay of 4 to 5 ns. When the configuration cell is turned off, the
slew rate is set for low-noise performance. Each I/O pin has an individual
EEPROM bit that controls the slew rate, allowing designers to specify the
slew rate on a pin-by-pin basis. The slew rate control affects both the rising
and falling edges of the output signal.
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Altera Corporation
INTEL [ INTEL ]
