I/O Structures in IGLOOe and Pro ASIC3E Devices

v1.4

25

At the system level, the skew circuit can be used in applications where transmission activities on

bidirectional data lines need to be coordinated. This circuit, when selected, provides a timing

margin that can prevent bus contention and subsequent data loss and/or transmitter over-stress

due to transmitter-to-transmitter current shorts. Figure 17 presents an example of the skew circuit

implementation in a bidirectional communication system. Figure 18 on page 26 shows how bus

contention is created, and Figure 19 on page 26 shows how it can be avoided with the skew

circuit.

Figure 15 • Timing Diagram (option 1: bypasses skew circuit)

Figure 16 • Timing Diagram (option 2: enables skew circuit)

ENABLE (IN)

ENABLE (OUT)

Less than

0.1 ns

Less than

0.1 ns

ENABLE (IN)

ENABLE (OUT)

1.2 ns

(typical)

Less than

0.1 ns

Figure 17 • Example of Implementation of Skew Circuits in Bidirectional Transmission Systems Using IGLOO or

ProASIC3 Devices

Transmitter 1: ProASIC3 I/O

Transmitter 2: Generic I/O

ENABLE(t2)

EN (b1)

EN (b2)

Routing

Delay (t1)

Routing

Delay (t2)

EN (r1)

ENABLE (t1)

Skew or

Bypass

Skew

Bidirectional Data Bus

Transmitter

ENABLE/

DISABLE