107
C4 Manual Rev 7.5.2
unlikely that a problem will cause a bad load, but it is possible and it’s the easiest
problem to fix, so try reloading first.
Starting the C4 from PROM based firmware
If reloading doesn’t work, you can try starting the controller from the older
firmware that permanently resides on the PROM in the controller. To initiate a
PROM based startup, press <START/STOP> rapidly three times while the model
number is displayed (very first display upon power up). This will cause the
controller to bypass the newly installed firmware and run from the older version.
COM port issues
If the update software on the PC won’t start due to communication problems, the
difficulty is likely either a bad/wrong cable, non standard COM port settings, or a
non standard UART. Check to be certain that you are using a standard modem
cable (straight through) and not a “null modem” cable (pins 2 & 3 crossed). If the
cable is not the problem, use a utility program such as Microsoft’s MSD or Norton
Utilities’ NDIAGS to test the PC’s COM ports and check the addresses, interrupt,
and UART number. COM1 should be located at address 3F8 with IRQ4, and
COM2 should be at address 2F8 with IRQ3. The UART should be an 8250 or a
number that starts with 16. Some early PCs used non standard UARTs and
address assignments and relied on the very slow system BIOS to keep all this
straight. The Sigma upload software bypasses the BIOS to achieve better
performance (19,200 baud) and cannot tolerate non standard COM ports.
If you’ve done all the above, and still have a problem, check the Sigma web site at
www.SigmaSystems.Com for service bulletins. If you still don’t have a solution,
your controller will likely need to be returned to Sigma for service.
9.8 Temperature Control (PID) Tuning & Problems
The Sigma C4 controller uses a classic PID control algorithm. Users who are
familiar with PID control will find this section somewhat simplistic and
generalized as it is written for use by support personnel who are competent
installers and mechanics, but who may not know, or need to know, the theory and
intricacies of PID control.
There are three user adjustable control “terms” that the C4 uses to control
temperature. They are: