Spark Logic

ADM485 half-duplex RS-485 transceiver connection guide

ADM485 half-duplex RS-485 transceiver MSOP-8 (RM-8) wiring guide with power, signal assignments, and bench checks.

SOIC-8 (R-8) 8 contacts
PDIP-8 (N-8) 8 contacts

MSOP-8 (RM-8)

8 contacts Current package

Analog Devices · Mini small-outline package.

Industrial, −40 to +85 °C.

Bring up the receiver

Required

Use 5 V logic for this fixture. Hold DE low and /RE low. Ground the unused DI input.

C1 100 nF between 5 V and Bus reference5 VC1 100 nFBus reference

Bench checks

  • With A and B open, the enabled receiver should drive RO high.

Analog Devices ADM485 Rev. F, Tables 5–6. Local bypass is a fixture choice.

Connection scenarios

Link two half-duplex nodes

Use two 5 V logic endpoints with a short 120 Ω twisted pair. On each node tie DE to /RE and pull the shared direction node low during controller reset. Use one 120 Ω termination at each end.

  • 5 V
  • Bus reference
  • Direction
  • UART transmit
  • UART receive
  • Pair A
    • A (6)
    • Peer noninverting bus terminal
    • RT.1
    • RT peer.1
  • Pair B
    • B (7)
    • Peer inverting bus terminal
    • RT.2
    • RT peer.2
C1 100 nF between 5 V and Bus reference5 VC1 100 nFBus reference
RT 120 Ω at each end between Pair A and Pair BPair ART 120 Ω at each endPair B
RPD 10 kΩ between Direction and Bus referenceDirectionRPD 10 kΩBus reference

Bench checks

  • Confirm only one driver is enabled at any time. Drop DE after the final stop bit leaves the UART.
  • Probe the differential pair while sending 0x55. A driven one gives positive A minus B.
  • The open-input state does not establish a guaranteed logic level for a terminated idle bus. Use protocol-appropriate bias or a receiver designed for that condition.

Analog Devices ADM485 Rev. F, Tables 4–6 and Applications Information. The two-node fixture uses 120 Ω cable.

MSOP-8 (RM-8) wiring map

Highlighted contacts are used in the required step or selected circuit. Select a contact to inspect it.

Top view. Locate the package index before counting counterclockwise from pin 1.
Selected pin details

7 · B

Bidirectional · Bidirectional

Inverting side of the differential pair.

Analog Devices ADM485 Rev. F, Table 6

Electrical limits · Pin in the reference

Models and documents

The eight contact assignments are shared by three packages with different mechanical drawings.

ADM485ARM
Industrial, −40 to +85 °C.
ADM485ARM-REEL
Industrial, −40 to +85 °C.
ADM485ARM-REEL7
Industrial, −40 to +85 °C.
ADM485ARMZ
Industrial, −40 to +85 °C.
ADM485ARMZ-REEL
Industrial, −40 to +85 °C.
ADM485ARMZ-REEL7
Industrial, −40 to +85 °C.