User`s manual
7.0 - Troubleshooting Section
Page - 64
In the background, PMAC executes one scan through an individual PLC program, then checks to see if there are any
complete commands, responding if there are, then executes the housekeeping functions. This cycle is repeatedly endlessly.
Most of the housekeeping functions are safety checks such as following error limits and overtravel limits. When it is done
with these checks, PMAC sets the 12-bit watchdog timer register back to its maximum value. As long as this occurs
regularly at least every 512 RTI cycles, the watchdog timer will not trip.
The purpose of this two-part control of the timer is to make sure all aspects of the PMAC software are being executed, both
in foreground (interrupt-driven) and background. If anything keeps either type of routine from executing, the watchdog will
fail quickly.
The only recover for this failure, assuming the 5 Volts power supply is satisfactory, is to hardware reset PMAC.
7.3 - Establishing communications
Either the Executive or Setup program can be used to establish initial communications with the card. Both programs have
menus that allow you to tell the PC where to expect to find the PMAC and how to communicate with it at that location. If
you tell it to look for PMAC on the bus, you must also tell it PMAC's base address on the bus (this was set up with jumpers
on PMAC). If you tell it to look for PMAC on a COM port, you must tell it the baud rate (this was set up with jumpers or
switches on the PMAC).
Once you have told the program where and how to communicate with PMAC, it will attempt to find PMAC at that address
by sending a query command and waiting for the response. If it gets the expected type of response, it will report that it has
found PMAC, and you will be able to proceed.
If it does not get the expected type of response after several attempts, it will report that it has not found PMAC, check the
following:
7.3.1 - General
1. Is the green LED (power indicator) on PMAC's CPU board ON, as it should be? If it is not, find out why PMAC is not
getting a +5V voltage supply.
2. Is the red LED (watchdog timer indicator) on PMAC's CPU board OFF, as it should be? If it is ON, make sure PMAC
is getting very close to 5V supply -- at less than 4.75V, the watchdog timer will trip, shutting down the card. The
voltage can be probed at pins 1 and 3 of the J8 connector (A1 and A2 on the PMAC-VME). If the voltage is
satisfactory, inspect PMAC to see that all inter-board connections and all socketed ICs are well seated. If you cannot
get the card to run with the red LED off, contact the factory.
7.3.2 - Bus Communications
1. Do the bus address jumpers (E91-E92, E66-E71) set an address that matches the bus address that the Executive
program is trying to communicate with?
2. Is there something else on the bus at the same address? Try changing the bus address to see if communications can be
established at a new address. Address 768 (300 hex) is usually open.
7.3.3 - Serial communications
1. Are you using the proper port on the PC? Make sure if the Executive program is addressing the COM1 port, that you
have cabled out of the COM1 connector.
2. Does the baud rate specified in the Executive program match the baud rate setting of the E44-E47 jumpers on
PMAC?
3. With a breakout box or oscilloscope, make sure you see action on the transmit lines from the PC as you type into the
Executive program. If you do not, there is a problem on the PC end.
4. Probe the return communication line while you give PMAC a command that requires a response (e.g. <CONTROL-
F>). If there is no action, you may have to change jumpers E9-E16 on PMAC to exchange the send and receive lines.
If there is action, but the host program does not receive characters, you may have RS-232 receiving circuitry that
does not respond at all to PMAC's RS-422 levels. If you have another model of PC, try using it as a test (most
models accept RS-422 levels quite well). If you cannot get your computer to accept the signals, you may need a
level-conversion device, such as Delta Tau's Accessory-26.