Johnson Controls Mercury 3 Series Hardware Installation page 8

CKM-MR52-S3
24-10707-198 Rev. –
Communications Wiring (SIO Communication Port)
The CKM-MR52 communicates to an intelligent controller (for example,
CKM-EP2500) via a 2-wire RS-485 interface. The CKM-MR52 allows
for multidrop communication on a bus of up to 4,000 feet (1,200 m). Use
twisted pairs (minimum 24 AWG) with drain wire and shield for
communication. See
Install RS-485 termination jumper, J4, on the interface boards at each end
of the communication line only.
Figure 3 shows the CKM-MR52 communications wiring.
Reader Wiring
Each reader port supports a reader with TTL (D1/D0, Clock/Data) or 2-wire
RS-485 signaling. Power to the reader is selectable: 12 VDC (VIN must be
greater than 20 VDC), or power is passed-through (PT) from the input voltage
of the MR52 (TB7-VIN), 300 mA maximum per reader port. Readers that
require different voltage or have high current requirements must be powered
separately. Refer to the reader manufacture specifications for cabling
requirements. In the 2-wire LED mode the buzzer output is used to drive the
second LED. Reader port configuration is set via the host software.
Specifications
Figure 3: CKM-MR52 Communications Wiring
4
Hardware Installation Manual
for details.