Delta Tau GEO BRICK LV User Manual

 

L: 

48 bits floating-point across both X- and Y-memory 

DP: 

32 bits fixed-point (low 16 bits of X and Y) (for use in dual-ported RAM) 

F: 

32 bits floating-point (low 16 bits of X and Y) (for use in dual-ported RAM) 

TWD:  Multiplexed BCD decoding from Thumbwheel port 

TWB:  Multiplexed binary decoding from Thumbwheel port 

TWS:  Multiplexed serial I/O decoding from Thumbwheel port 

TWR:  Multiplexed serial resolver decoding from Thumbwheel port 

*: 

No address definition; uses part of the definition word as general- 

 purpose 

variable 

If an X or Y type of M-variable is defined, you must also define the starting bit to use, the number of bits, 
and the format (decoding method). 
Typical M-variable definition statements are: 

See the instructions for each type of M-variable definition in the On-Line Commands reference section of 
the manual.  This can be found in the Talking to Turbo PMAC section of this manual.  Many suggested 
M-variable definitions are given in the software reference manual as well. 

It is a good idea to prepare a single file with all of your M-variable definitions and to put at the top of this 
file the command M0..8191->*.  This will remove all existing definitions, and help to prevent 
mysterious problems caused by “stray” M-variable definitions. 

The M-variable definitions are stored as 48-bit codes at Turbo PMAC memory addresses $004000 (for 
M0) to $005FFF (for M8191).  The Y-register contains the address of the register pointed to by the 
definition; the X-register contains a code that determines what part of the register is used and how it is 
interpreted. 

If another M-variable points to the Y-register, it can be used to change the subject register.  The main use 
of this technique is to create arrays of registers, which can be used to walk through tables in memory. 

Limited Range 

Many M-variables have a more limited range than Turbo PMAC’s full computational range.  If a value 
outside of the range of an M-variable is placed to that M-variable, Turbo PMAC rolls over the value 
automatically to within that range and does not report any errors. 

For example, with a single bit M-variable, any odd number written to the variable ends up as 1, any even 
number ends up as 0.  If an attempt is made to place a non-integer value in an integer M-variable, Turbo 
PMAC automatically rounds to the nearest integer. 

Using M-Variables 

Once defined, an M-variable may be used in programs just as any other variable – through expressions.  
When the expression is evaluated, Turbo PMAC reads the defined memory location, calculates a value 
based on the defined size and format, and utilizes it in the expression. 

Care should be exercised in using M-variables in expressions.  If an M-variable is something that can be 
changed by a servo routine (such as instantaneous commanded position), which operates at a higher 
priority than the background expression evaluation, there is no guarantee that the value will not change in 
the middle of the evaluation.  For instance, if in the expression