PMAC Quick Reference Guide For I-Variables with limited range, an attempt to assign an out-of-range value does not cause an error. The value is rolled over automatically to within the range by modulo arithmetic (truncation). For example, I3 has a range of 0 to 3 (4 possible values). The command I3=5 would actually assign a value of 5 modulo 4 = 1 to the variable. On PMACs with battery-backed RAM, most of the I-Variable values can be stored in a 2K x 8 EEPROM IC with the SAVE command. These values are safe here even in the event of a battery-backed RAM failure, so the basic setup of the board is not lost.
After a new value is given to one of these I-Variables, the SAVE command must be issued in order for this value to survive a power-down or reset. The I-Variables that are not saved to EEPROM are held in battery-backed RAM. These variables do not require a SAVE command to be held through a power-down or reset, and the previous value is not retained anywhere. These variables are: I19-I44, Ix13, Ix14. On PMACs with flash memory backup (those with Option 4A, 5A, or 5B), all of the I-Variable values can be stored in the flash memory with the SAVE command. If there is an EEPROM IC on the board, it is not used.
After a new value is given to any I-Variable, the SAVE command must be issued in order for this value to survive a power-down or reset. Default values for all I-Variables are contained in the manufacturer-supplied firmware. They can be used individually with the I{constant}=* command, or in a range with the I{constant}.. {constant}=* command. Upon board re-initialization by the $$$*** command or by a reset with E51 in the non-default setting, all default settings are copied from the firmware into active memory. The last saved values are not lost; they are just not used. P-Variables P-Variables are general-purpose user variables.
They are 48-bit floating-point variables at fixed locations in PMAC’s memory, but with no pre-defined use. There are 1024 P-Variables, from P0 to P1023. A given P-Variable means the same thing from any context within the card; all coordinate systems have access to all P-Variables (contrast Q-Variables, which are coupled to a given coordinate system). This allows for useful information passing between different coordinate systems. P-Variables can be used in programs for any purpose desired: positions, distances, velocities, times, modes, angles, intermediate calculations, etc. If a command consisting simply of a constant value is sent to PMAC, PMAC assigns that value to variable P0.
For example, if the command 342 is sent to PMAC, it will interpret it as P0=342 . This capability is intended to facilitate simple operator terminal interfaces. It does mean, however, that it is not a good idea to use P0 for other purposes, because it is easy to change this accidentally. Q-Variables Q-Variables, like P-Variables, are general-purpose user variables: 48-bit floating-point variables at fixed locations in memory, with no pre-defined use. However, the meaning of a given Q-Variable (and hence the value contained in it) is dependent on which coordinate system is utilizing it.
This allows several coordinate systems to use the same program (for instance, containing the line X(Q1+25) Y(Q2), but to do have different values in their own Q-Variables (which in this case, means different destination points). Several Q-variables have special uses. The ATAN2 (two-argument arctangent) function uses Q0 automatically as its second argument (the cosine argument). The READ command places the values it reads following letters A through Z in Q101 to Q126, respectively, and a mask word denoting which variables have been read in Q100. The S (spindle) statement in a motion program places the value following it into Q127.
Based on that and since a total of 1024 Q-Variables are shared between potentially eight Coordinate Systems (128 variables each), the practical range of the Q-Variables to be used safely in motion programs is therefore Q1 to Q99. Programming PMAC 33