| Number | Name | Date | Kind |
|---|---|---|---|
| 4757533 | Allen et al. | Jul 1988 | |
| 4787027 | Prugh et al. | Nov 1988 | |
| 4800590 | Vaughan | Jan 1989 | |
| 4850899 | Maynard | Jul 1989 | |
| 4891636 | Ricker | Jan 1990 | |
| 4951249 | McClung et al. | Aug 1990 | |
| 4972470 | Farago | Nov 1990 |
| Number | Date | Country |
|---|---|---|
| 0158072 | Jun 1990 | JPX |
| Entry |
|---|
| Anonymous; "Port Extender"; Research Disclosure, Jan. 1991, No. 321, K. Mason Publications. |