AFS090 datasheet(169/334 Pages) MICROSEMI

169 / 334 page

Fusion Family of Mixed Signal FPGAs

R e visio n 2

2 - 153

Weak Pull-Up and Weak Pull-Down Resistors

Fusion devices support optional weak pull-up and pull-down resistors for each I/O pin. When the I/O is

pulled up, it is connected to the VCCI of its corresponding I/O bank. When it is pulled down, it is

connected to GND. Refer to Table 2-97 on page 2-173 for more information.

Slew Rate Control and Drive Strength

Fusion devices support output slew rate control: high and low. The high slew rate option is recommended

to minimize the propagation delay. This high-speed option may introduce noise into the system if

appropriate signal integrity measures are not adopted. Selecting a low slew rate reduces this kind of

noise but adds some delays in the system. Low slew rate is recommended when bus transients are

expected. Drive strength should also be selected according to the design requirements and noise

immunity of the system.

The output slew rate and multiple drive strength controls are available in LVTTL/LVCMOS 3.3 V,

LVCMOS 2.5 V, LVCMOS 2.5 V / 5.0 V input, LVCMOS 1.8 V, and LVCMOS 1.5 V. All other I/O

standards have a high output slew rate by default.

For Fusion slew rate and drive strength specifications, refer to the appropriate I/O bank table:

•

Fusion Standard I/O (Table 2-78 on page 2-154)

•

Fusion Advanced I/O (Table 2-79 on page 2-154)

•

Fusion Pro I/O (Table 2-80 on page 2-154)

Table 2-83 on page 2-157 lists the default values for the above selectable I/O attributes as well as those

that are preset for each I/O standard.

Figure 2-110 • Timing Diagram (with skew circuit selected)

EN (b1)

EN (b2)

Transmitter 1: ON

ENABLE (t2)

Transmitter 2: ON

Transmitter 2: OFF

ENABLE (t1)

Result: No Bus Contention

Transmitter 1: OFF

AFS090 Datasheet(PDF) 169 Page - Microsemi Corporation