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PMAC Dual-Ported RAM User Manual

Dual-Ported RAM Communications 9

M130->D:$28 ;motor #1 actual position

M131->DP:$D000 ;point to a location in DPRAM

OPEN PLC 1 CLEAR

M131=M130/(I108*32) ;update motor position (in counts) in DPRAM

I5=2 ; allow PLC 1 to be enabled

ENABLE PLC 1 ; “turn on” PLC 1

Now, read the location corresponding to M131 ($D000 in PMAC's memory) in PC memory and extract

this position information so that the C program can use it. The corresponding address in PC memory can

easily be determined by talking the address location in PMAC’s memory minus the starting address

(always $D000), multiply by 4 (because the X and Y words for each location in PMAC’s DPRAM space

is equivalent to four bytes or locations of PC memory) and add it to the PC memory starting address

selected for the DPRAM.

PC Location = ((PMAC Mem. Location (hex)- $D000)

4) + (PC Mem Starting Address selected for DPRAM)

Assume we configured DPRAM to start at PC address $D4000. We want the equivalent PC address

location for PMAC location $D200. This would be:

Hex: ($D200 -$D000)

× 4 + $D4000 = $D4800

Decimal: (53760 - 53248)

× 4 + 868352 = 870400

Our C code now only has to PEEK location $D4800 and $D4802 (since we need to get four bytes to get a

32 bit word) to obtain motor #1’s current position. The C code subroutine may look like this.

long get_motor_position (){

int hi_word;

unsigned lo_word;

lo_word = peek (0xD400, 0x0800);

hi_word = peek (0xD400, 0x0802);

return (hi_word *65536 +lo_word);

Example #2: To calculate positions for three axes in a custom C program and have PMAC move to these

positions. Assign three M-variables to point to three DPRAM locations, write position values to these

locations with the C program, and have a PMAC motion program use these variables in its move

statements. In the sample code below, a flag bit has been used to signal the C program when the data has

been taken by PMAC so the next move locations can be loaded.

M101->DP:$D201 ; used for motor x’s commanded position

M102->DP:$D202 ; used for motor x’s commanded position

M103->DP:$D100 ; used for motor x’s commanded position

M100->DP:$D200,0 ; go flag to stop motion program

M104->DP:$D200,1 ; flag to stop C program when positions have

; been received

OPEN PROG 1 CLEAR

TA10

WHILE(M100=1) ;keep looking while go flag is 1

X(M101) Y(M102) Z(M103) ;move x,y,z to new positions

ENDWHILE

The C program calculates the positions, and would send them to PMAC via a subroutine like this:

void update_positions (longx, long y, long z, int stop_program)

{

static long far *x, *y, *z;

x = MK_FP (0xD400, 0x0804);

y = MK_FP (0xD400, 0x0808);

z = MK_FP (0xD400, 0x080C);