Reference Manual

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PMAC 2 Software Reference

24 PMAC I-Variable Specifiation

PMAC-to-Host Checksum: PMAC will compute the checksum of any communications

line it sends to the host. This checksum includes

control characters sent with the line,

including the final <carriage-return>. The checksum is sent immediately following

this <carriage-return>. On a multiple-line response, one checksum is sent for each

line. Note that this checksum is sent before the checksum of the command line that caused

the response.

For more details on checksum, refer to the Writing a Host Communications Program

section of the manual.

Serial

character errors: If PMAC detects a serial character error, it will set a flag so that

the entire command line will be rejected as having a syntax error after the <CR> is sent.

With I4=0 or 1, it will also send a <BELL> character to the host immediately on detecting

the character error. Note that this mode will catch a character error on the <CR> as well,

whereas in the I4=2 or 3 mode, the host would have to catch an error on the <CR>

character by the fact that PMAC would not respond (because it never saw a <CR>).

See Also

Communications Checksum (Writing a Host Communications Program)

I-variables I3, I6

On-line command <CTRL-N>

Jumper E49

I5 PLC Programs On/Off

Range

0 .. 3

Units

none

Default

Remarks

I5 controls which PLC programs may be enabled. There are two types of PLC programs:

the foreground programs (interpreted PLC 0 and compiled PLCC 0), which operate at the

end of servo interrupt calculations, with a repetition rate determined by I8 (PLC 0 should

be used only for time-critical tasks and should be short); and the background programs

(interpreted PLC 1 to PLC 31 and compiled PLCC1 to PLCC 31) which cycle repeatedly

in background as time allows. I5 controls these as follows:

Setting Meaning

0 Foreground PLCs off; background PLCs off

1 Foreground PLCs on; background PLCs off

2 Foreground PLCs off; background PLCs on

3 Foreground PLCs on; background PLCs on

Note that an individual PLC program still needs to be enabled to run – a proper value of I5

merely permits

it to be run. Any PLC program that exists at power-up or reset is

automatically enabled (even if the saved value of I5 does not permit it to run immediately);

also, the ENABLE PLC n or ENABLE PLCC n command enables the specified

program(s). A PLC program is disabled either by the DISABLE PLC n or DISABLE

PLCC n command, or by the OPEN PLC n command. A CLOSE command does not

automatically re-enable an interpreted PLC program – it must be done explicitly. When

the compiled code for PLCC programs is downloaded to the PMAC, they are automatically

enabled if permitted by I5.