Cypress Computer Systems EXP-2000 SUPREX Reader Expansion Module for SPX and HHR products (not compatible with SPX-1300). RS-485 Interface. Includes Central and Remote units. Supports reader and 2 relays with LED, door hardware and associated I/O. Requires 8 - 16 VDC. Durable aluminum housing. Overall dimensions of each unit: 4.50" x 2.90" x 1.00" (approx).Firmware version 400 and newer are not compatible with SPX units made before May 2016 (Serial Number 126055 or lower).