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RS-232 Resources for TestEquity Chambers with the F4 Controller

TestEquity chambers use programmable controllers which are manufactured by Watlow Electric. The F4 Controller's native interface is RS-232 and use the Modbus RTU protocol.

This page is applicable to the legacy F4 Controller with up/down arrow keys, NOT the F4T Touch Screen Controller.

Sample 16-bit Modbus Packet
Modbus_Packet.pdf (209K) illustrates sample 16-bit Modbus packets to write a temperature set point and read the actual temperature. See Modbus Registers below for a list of the most common registers you will need to read from or write to.

Modbus Industry Organization
Visit http://www.modbus.org for a more information about the Modbus RTU interface.

Python
See MinimalModbus for programming Modbus RTU in Python. See Modbus Registers below for a list of the most common registers you will need to read from or write to.

Visual Basic Programming Examples from Watlow
Example of Communications in Modbus RTU Using Visual Basic, WatlowMB.zip (23K).

LabVEIW Drivers
Drivers are available on the NI Driver Network. These drivers are generic and were NOT developed by TestEquity.

Modbus Registers

Every controller function has a corresponding "register" number which can be read or written to (when applicable). The complete list of registers are listed Chapter Seven of the Series F4 User's Manual (pdf, 4M) . However, 95% of all automated test applications require knowledg of just the few common registers listed bellow.

Common Modbus Registers

  • The actual chamber temperature reading is Modbus register 100 (Input 1 Value).
  • The actual chamber humidity reading is Modbus register 104 (Input 2 Value, for Humidity Chambers only).
  • The static temperature set point is Modbus register 300 (Set Point 1).
  • The static humidity set point is Modbus register 319 (Set Point 2, for Humidity Chambers only).
  • The temperature set point during a profile is Modbus register 4122 (Set Point 1, Current Profile Status).
  • The humidity set point during a profile is Modbus register 4123 (Set Point 2, Current Profile Status, for Humidity Chambers only).
  • The decimal points are implied. For example, 1005 is actually 100.5 and -230 is -23.0.
  • The Digital Output 1 (Event 1) function is Modbus register 2000. Write 0 for OFF, 1 for ON.
  • The Digital Output 2 (Event 2) function is Modbus register 2010. Write 0 for OFF, 1 for ON.
  • The Digital Output 3 (Event 3) function is Modbus register 2020. Write 0 for OFF, 1 for ON.

RS-232 Troubleshooting Tips

We receive many calls each week regarding RS-232 communication issues. There are several issues which must be addressed in order to communicate successfully with the chamber. With thousands of chambers in the field, we have never had a verified case of a bad serial interface in the controller. Below are several of the most common communication issues.

Are you using the correct cable?
The DB-9 connector is wired to accommodate a null-modem cable. A null-modem cable has pins 2 and 3 swapped on each end. You CANNOT use a straight through cable.

Null-Modem Cable

Is the baud rate set correctly?
All TestEquity chambers shipped since mid-2003 have the baud rate set at 9600. Older chambers have the baud rate set at 19200. The baud rate of the controller MUST match the baud rate in your communications program. The baud rate is changed in the controller's Go to Setup\Communications menu. You may require a password to enter the Setup menu. If so, call TestEquity to get the password.

Does your software communicate using the Modbus RTU protocol?
To communicate with the controller from a PC, you need to run software that uses the Modbus RTU protocol. You CANNOT use Hyperterminal. You CANNOT send simple ASCII or SCPI commands directly to the chamber's RS-232 interface.