A port replicator duplicates externally and extends features that are already available in a mobile PC — for example, providing an extra PC Card slot.
A port replicator with dedicated features allows the end user to add a specific feature to the original mobile PC — for example, providing a CD-ROM drive when the mobile unit does not have such a drive.
A mobile PC with a port replicator does not need to meet the expansion card requirements defined for Basic PC 97, and also does not need to meet all the resource requirements of a mobile/docking station combination. A port replicator is not required to provide an undock or eject button.
However, some mobile PC system designs include a port replicator that has dedicated features for networking, additional PC Card slots, CD-ROM, and so on. This means that the system could have additional resource requirements so that all available IRQs in the system are already allocated; and therefore the PC Card slots (for example) would not have any IRQs available, rendering them useless. In such cases, the port replicator must contain devices that replace any devices in the mobile PC that do not meet the resource requirements for a PC 97 computer.
54. Automatic resource assignment and dynamic disable capabilities for replacement devices
| Required |
A port replicator that can accept expansion cards must contain devices that replace any devices in the mobile PC that do not meet Basic PC 97 requirements for IRQ, DMA, I/O port, and memory resources. This allows the operating system to disable the device on the mobile PC, enable the corresponding device on the port replicator, and then arbitrate resources among the remaining devices in the mobile unit and the devices on the port replicator.
Devices in the system must be capable of being disabled dynamically, so that the user can choose to free resources in order to allow other devices in the system to function. For ISA devices included with the PC system that do not otherwise meet the resource requirements defined for PC 97, the system designer must implement IRQ sharing for ISA, as described in the "ISA" chapter in Part 3 of this guide.