Quickstart Guide
ABB PLC and drives integration using Modbus RTU
ModbusRTU‐7‐ PLCanddrivesintegration
AC500andAC500eCoCOMportoverview
AC500 AC500‐eCo CM574‐RS
COM1 COM2 COM1 COM2
(optional)
COM1=COM2
(seeCOM1of
AC500,exceptpull‐
up/pull‐down)
COMVoltagelevel 5V 5V 3,3V 3,3V 5V
Opto‐isolated
(electricallyisolated)
YES YES NO
optional*)
NO YES
Maximumbuscable
length
Acc.toRS485
standard
Acc.toRS485
standard
50m
*)Accto
RS485
standard
50m Acc.toRS485
standard
Connection Terminal 9poleD‐sub 9poleD‐sub
*)Terminal
Terminal Terminal
Terminationresistor
built‐in
NO NO NO NO NO
Terminationresistor
size
120Ω 120Ω 120Ω 120Ω 120Ω
Pull‐up/pull‐down
resistorsbuilt‐in
YES(connect
withbridges)
NO NO
*)yesconnect
withbridges
YES(connect
withbridges)
YES(connectwith
bridges)
Pull‐up/pull‐down
resistorsize
470Ω 470Ω 270Ω 270Ω 475Ω
Pull‐up/pull‐down
resistorsconnection
point
Master(CPU)
COMport
Master(CPU)
COMport
Master(CPU)
COMport
Master
(CPU)COM
port
Master(CPU)COM
port
Pull‐up/pull‐down
connection
Bridges:1to
2and3to4
External470
Ωresistors
External270Ω
resistors
Bridges:1to
2and3to4
Bridges:1to2and3
to4
*)usingTK506RS485isolatorforPM554/PM564withindexA3andhigher
Driveswithembeddedfieldbus
ThefollowingABBdriveshaveModbusRTUembedded:
ACS310
ACS/ACH550
ACS850
Since the built‐in end termination of the drive automatically also activates pull‐up/pull‐down resistors, it is
recommendedtoskipthebuilt‐inoption.
Itis recommended to connect a separateendtermination resistor to the first node (i
.e.thePLC COM interface)
andthelastnode(i.e.thelastdriveonthebus).
Forconnectionexamples,seechapter“Installationexamples”.
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