12.1 Layout Guidelines

The stub length from the VMEH22501 to the connector should be as short as possible. To reduce system skew, stub lengths should be matched for all the data and control bits. Populating both sides of the daughter card may help optimize the stub lengths.

The 5-row connector and the 3-row connector specifications correspond completely. All the data and control lines have the same pin positions in these two connectors. This allows easy migration from a 3-row connector to a 5-row connector. If a 5-row connector is used instead of a 3-row connector, some bypass capacitors between the supply pins and GND of the external rows (at the back of the connector) will help reduce some ground-bounce noise.

TI recommends to use multiple bypass capacitors to stabilize the supply line. To reduce high-frequency noise, TI recommends a small capacitor (0.1 µF, or less) for every two VCC pins on the VME side of the VMEH22501. The capacitors should be as close as possible to the VCC pins. An additional large capacitor close to the chip helps maintain the dc level of the power-supply line.

If live insertion is required, TI recommends a specific power-up sequence to use the full live-insertion capability of the VMEH22501. The power-up sequence should be GND, BIAS VCC, OE pin, I/O ports, then VCC.

12.2 Layout Example

Figure 15. Layout Recommendation