MKS P9B, Instruction Manual, Page: 54 / 112

Chapter Four: Analog and Digital Interface Digital Interface Input and Output Options
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
Device is powered at operating temperature, preferably for 30 or more minutes.

Devices subject to ambient temperatures other than room temperature (23º C) should be zeroed under
those conditions.

Pressure drop and flow across the device is reduced to zero. Depending on the gas panel configuration,
this may be done by one of the referenced procedures. See Chapter 7 “Maintenance” for zeroing
procedures.
RS485 Digital Interface Using 9 Pin D Male Connector
The RS485 MFC has one 9 pin D male connector that provides the communications interface with the RS485
master slave network, electrical power from the network bus, and shielding for the instrument signals. There
are no analog I/O signals on this device.
Table 12: Digital Interface – RS485 Using 9 Pin D – Model Code 5
Pin 1 No Connection
Pin 2 No Connection
Pin 3 + 11 to 25 VDC Power In
Pin 4 Power Return
Pin 5 No Connection
Pin 6 RS485 Return
Pin 7 RS485 +
Pin 8 RS485 -
Pin 9 Shield
RS485 Communications Protocol
The MFC controller acts as a slave device on an RS485 multi-drop bus. It continually listens for transaction
requests from the host controller, processes requests addressed to it, and sends replies as needed. For a
complete description of this multi-drop protocol see the MKS Document, RS485 command document,
1042928-001, “Supplement, RS485 Command Specifications, P9B MFC”. Please contact MKS for this
document.
RS485 Controls and Indicators
The top panel of the MFC contains several controls and indicators.
Table 13: RS485 Module Status LED Indicators
LED Status Meaning
Flashing Red The device is online and functioning properly.
The Module Status LED flashes red when receiving commands from Host.
Solid Red Critical link failure.
The device has detected an error that prevents network communication (Duplicate
MAC_ID or bus-off.)
Dark Not powered / Not online.
The device is offline or the device is not powered; check the network status LED.