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PMAC 2 Software Reference

32 PMAC I-Variable Specifiation

Note:

The BREQ line to the interrupt controller reflects the status of the

hardware-selected coordinate system (by JPAN pins FPDn/) if the

control-panel inputs are enabled (I2=0); it represents the status of

the software-host-addressed coordinate system if the control-panel

inputs are disabled (I2=1). In virtually all applications using this

feature, the user will want to set I2 to 1 so the BREQ line reflects

the status of the coordinate system to which he is currently talking.

Example

With I17=10 and I16=5, as program lines are sent to PMAC, PMAC will keep requesting

more lines (BREQ goes high, Rotary Buffer Full bit stays 0) until there are 10 lines in the

buffer ahead of the executing line. BREQ will then be held low and Rotary Buffer Full bit

stays 1 until enough program lines have executed so that there are less than 5 lines in the

buffer ahead of the execution point. At this time, BREQ will be set high again, and Rotary

Buffer Full will become 0.

See Also

Using Interrupts (Writing a Host Communications Program)

Rotary Motion Program Buffers (Writing a Motion Program)

Coordinate-system Rotary Buffer Full status bit (Y:$0817, etc., bit 16)

On-line commands PR, ??

I-variables I2, I17, I18

I17 Rotary Buffer Request Off Point

Range

0 .. 8,388,607

Units

Program lines

Default

Remarks

I17 controls how many lines ahead of the executing line the host can provide a PMAC

rotary motion program buffer before it signals that it is not ready for more lines (BREQ

line held low, coordinate system status bit Rotary Buffer Full becomes 1). This status

information can be detected either by polling (??or PR) or by using the interrupt line to

the host.

If you send a program line to the rotary buffer, the BREQ line will be taken low (at least

momentarily). If there are still fewer than I17 number of lines in the buffer ahead of the

executing line, the BREQ line will be taken high again (giving the ability to generate an

interrupt), and the Rotary Buffer Full status bit will stay 0. If there are greater than or

equal to I17 lines in the buffer ahead of the executing line, the BREQ line will be left low,

and the Rotary Buffer Full status bit will become 1.

Normally at this point, the host will stop sending program lines (although this is not

required) and wait for program execution to catch up to within I16 lines and take BREQ

high again.