The Sentry Model HM-501 Dual Serial Interface Card provides 2 serial data channels utilizing RS-485 or RS422 data standards.  Each channel can be independently addressed and configured for half-duplex (RS-485) or full-duplex (RS-422) operation.   Jumpers are provided to choose the type of communication (half/full-duplex) and IRQ if required. 

Each, port when configured for half-duplex operation, can communicate with 63 addressed Sentry devices, such as Host Panels (Model HM-527), Utility Panels (Models HM-610/612), and Power Supplies (Model HM- 535).  Alternately, the port can communicate with a maximum of 16 Remote LCD Displays Model HM-676).

Each port can also be configured for full-duplex communication for use in Sentry systems requiring Host - Remote Console communication

The Model HM-501 communicates with differential data signals following the EIA standards described for RS-485 / RS-422. A typical data line can extend over 4000 feet and does not require special line terminations.

The dual channel card is equipped with two 9 pin sub D connectors with the pin out connections detailed in the HM-501 Installation and Service Manual. 

To estimate the number of Dual Serial cards required for a particular   installation, refer to the Model HM-550 Master Controller Technical Specification.   For installations with greater than 416 apartments, the Model HM-502 Quad Serial Interface Card or Model HM-503 Quad Isolated Serial Interface Card should be used, contact the factory for details.