## Input/Output Device Driver Reference

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### IBM PS/2 (with Micro Channel) Considerations for COM1-4

The IBM PS/2 ASYNC device driver has device names COM1, COM2, COM3, and COM4 in its device driver header. Device name COM1 corresponds to the first LID in the ABIOS common data area with the ASYNC Device ID. Device name COM2 corresponds to the second LID. Device name COM3 corresponds to the third LID. Device name COM4 corresponds to the fourth LID in the ABIOS common data area with the ASYNC Device ID.

The Advanced BIOS architecture ensures that the ordering in the ROM BIOS 40 : data area matches the ordering of the LIDs in the common data area. Compatibility BIOS supports up to four ASYNC devices on the IBM PS/2 system , and the physical device driver assumes that the order of the Logical IDs matches the order of the addresses of these devices in the ROM BIOS 40: data area. Additional ASYNC devices can be supported by additional device drivers.

The mapping of the ASYNC Logical ID ordering to COMn must be consistent across all device drivers that support the ASYNC hardware in the IBM PS/2 hardware environment.