# MR52 — Downstream Reader Interface

## Overview

The Mercury MR52 is a downstream reader interface module used to expand a Mercury panel with additional reader ports. It adds 2 readers and 4 supervised inputs per module. Typically used with an EP1502 or similar host controller to support additional doors without a full second panel.

<table id="bkmrk-specvaluereaders2-%28w"><thead><tr><th>Spec</th><th>Value</th></tr></thead><tbody><tr><td>Readers</td><td>2 (Wiegand or OSDP)</td></tr><tr><td>Inputs</td><td>4 supervised</td></tr><tr><td>Outputs</td><td>2 relay</td></tr><tr><td>Communication</td><td>RS-485 downstream from host panel</td></tr><tr><td>Power Input</td><td>12VDC from host or separate supply</td></tr></tbody></table>

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## DIP Switches

The MR52 uses DIP switches to set its downstream RS-485 address relative to the host panel. Multiple MR52 modules can be chained from a single host.

<table id="bkmrk-addresssw1sw2sw3sw41"><thead><tr><th>Address</th><th>SW1</th><th>SW2</th><th>SW3</th><th>SW4</th></tr></thead><tbody><tr><td>1</td><td>ON</td><td>OFF</td><td>OFF</td><td>OFF</td></tr><tr><td>2</td><td>OFF</td><td>ON</td><td>OFF</td><td>OFF</td></tr><tr><td>3</td><td>ON</td><td>ON</td><td>OFF</td><td>OFF</td></tr><tr><td>4</td><td>OFF</td><td>OFF</td><td>ON</td><td>OFF</td></tr><tr><td>5</td><td>ON</td><td>OFF</td><td>ON</td><td>OFF</td></tr><tr><td>6</td><td>OFF</td><td>ON</td><td>ON</td><td>OFF</td></tr><tr><td>7</td><td>ON</td><td>ON</td><td>ON</td><td>OFF</td></tr></tbody></table>

**Address 0** (all OFF) is not valid — each MR52 must have a unique address. **SW5–SW8:** Reserved — leave OFF.

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## Wiring Notes

- **Downstream RS-485:** Connect the MR52 A(+)/B(−) to the downstream RS-485 port on the host Mercury panel (not the upstream network port). This is a separate bus from the host-to-controller RS-485.
- **Termination:** Place a 120Ω termination resistor on the last MR52 in the chain.
- **Power:** 12VDC — can share the host panel power supply if within budget, or use dedicated 12V supply for longer runs.
- **Readers:** R1 and R2 — connect same as a standard Mercury panel reader port (Wiegand or OSDP).
- **Inputs:** 4 supervised inputs — typically used for door contact (Input 1) and Rex (Input 2) for each reader, plus auxiliary inputs.

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## Common Use Cases

- Adding a second reader to a door (exit reader) where the host panel reader port is already used
- Expanding a single-door panel to handle additional monitoring points without adding a full panel
- Connecting readers in a remote location (elevator lobby, parking gate) with a longer RS-485 run

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## Resources

- [MR52 Installation Guide (HID/Mercury)](https://www.hidglobal.com/sites/default/files/resource_files/plt-03374_a_-_mr52_installation_guide.pdf)
- [Mercury Installation Assistant Utility (IAU)](https://downloadcenter.genetec.com/support/Firmware/Mercury/Mercury_IAU_FWTool_ver1043.zip)