There are two versions of the 12-port Serial Data Interface card.
Version 2 has four connectors that support three serial data ports each. Each port grouping can be configured for V.35, RS-232, or X.21 operation. When a port has been configured for a specific interface type, the other two ports in that same grouping must be configured for the same type. The card also supports an RS-530 interface with the use of an adapter cable that connects to a DB15 connector on the front of the X.21 distribution panel. There is no configuration specifically for the RS-530 interface; configuration is done in X.21 mode and applies to the RS-530 interface when it is physically enabled through hardware. All X.21 functionality is available on the RS-530 interface, except that only DCE operation is supported for RS-530. However, because X.21 does not support all the control leads available for RS-530, only a subset of the RS-530 control leads are supported.
The 12-port Serial Data Interface card, version 3, has six connectors that support two data ports each. Each port grouping can be configured for V.35, RS-232, X.21, or RS-530 operation. When a port has been configured for a specific interface type, the other port in the group must be configured for the same type.
Channelization on the 12-port Serial Data Interface card is supported down to the DS0 level.